PHY 100 (26-34) Pt. 4

through a particular medium. - Surface waves: Seismic waves that remain on the surface; they are responsible for much of the seismic damage caused in an earthquake. As a child, I would spend hours with my sisters and friends digging huge holes in the ground—as my father put it, “trying to dig to China.” However, my goals were not that lofty—I was just trying to get to the center of the Earth. And today, if it’s not too hot or too cold, you can probably find my friend's children digging in the backyard. In their case, though, they aren’t trying to dig to the core, just to the water table. (When I was a kid in SC, I did hit the water table, and I'm sure that's the only reason I couldn't get to the Earth's core). But we are in good company. Two of the deepest manmade holes in Earth are found in Russia. The Kola Superdeep Borehole is 12.26 km deep, and the Sakhalin-I Odoptu OP-11 well, completed in 2011, is 12.35 km deep. While they certainly have reached the water table, neither of these holes has even made it close to the bottom of Earth’s crust. But in drilling into the crust this deep, we have gained useful information about the interior of the Earth. Let’s look at what we know. The average density of Earth is about 5.5 g/cm3. If you are curious and want to see how this is determined, here are the calculations (Links to an external site.). If we look at the densities of the most abundant substances on Earth, we would include water and rocks. Here are the densities of these materials: SUBSTANCE DENSITY Water 1.0 g/cm3 Granite (representative of continental crust) 2.7 g/cm3 Basalt (oceanic crust) 3.0 g/cm3 Peridotite (mantle) 3.3 g/cm3 1) Most rocks found at the surface of the earth are less dense than the entire planet. (Select one answer.) A look at these numbers indicates that something is missing in our table. The density of Earth must increase as depth increases. The question is, how does the density increase? There are two models, as you can see in Figure 26.3 in your textbook or my more cartoonish version below. The density either increases gradually, as shown by the left side of the figure, or increases in abrupt layers, as shown on the right side of the figure. Your textbook also discusses evidence obtained from meteorites . The densities of the different types of meteorites, as well as the theory about how the meteorites were formed, also support the idea that density increases Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Note that S waves stop at the outer core. Remember, this is how we infer that the outer core is liquid. The increase in speed of P waves at the top of the inner core leads us to believe that it is solid. From seismic activity, we know that the Earth is composed of distinct layers. Crust We can see the crust, so we know the continental crust is, on average, granitic in composition. The oceanic crust, though, is basaltic. Both granite and basalt are types of silicates (For a review of silicates, see Lesson 24). Mantle Pieces of the upper mantle that have been carried up to the surface in volcanic eruptions have been found. These pieces are a relatively dense silicate called peridotite. Also, about 80% of the meteorites that fall to the Earth are stony meteorites that have an approximate peridotitic composition. It’s believed that these meteorites represent remnants of planet-sized parent bodies disrupted in the early history of the solar system and that are now orbiting the sun. Laboratory experiments indicate that peridotite is unstable at the conditions of the lower mantle called the mesosphere . At these conditions, peridotite undergoes chemical reactions that yield compounds called dense oxides that have denser packing of atoms. This accounts for the seismic discontinuities within the mesosphere. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

- Continental rift: A divergent plate boundary that occurs under continental crust. It is characterized by volcanic activity, frequent and severe earthquakes, and rift valleys. Eventually new oceanic crust will form as well as a new sea and then ocean. - Hot spot: Volcanic activity that results from the lithosphere moving over a mantle plume. Examples include Hawaii, Yellowstone, Iceland, and Samoa. - Island arc: A chain of volcanoes, shaped like an arc, that forms at an oceanic-oceanic convergent plate boundary. - Mantle plume: A buoyant mass of hot rock rising through Earth’s mantle. As it nears the surface of Earth, some of the plume melts and erupts at the surface, forming a hot spot. - Oceanic rift: A divergent plate boundary that occurs under oceanic crust. It is characterized by volcanic activity, frequent mild earthquakes, and a central rift valley. - Ridge push: Helps move Earth’s plates. The ridge is high and has gravitational potential energy that is converted into kinetic energy as the plate moves down the ridge. - Rift valley: A long, linear depression that commonly forms along a divergent plate boundary. - Slab pull: Helps move Earth’s plates. As an oceanic plate becomes old, cold, and dense, it sinks back into the mantle at a trench and pulls the rest of the plate along with it. - Subduction: The moving of an oceanic plate into the mantle as the plate moves under another lithospheric plate. - Transform fault: The break in Earth’s lithosphere that connects segments of ridges, trenches, or other plate boundaries that are sliding past each other together. The San Andreas Fault in California and the Alpine Fault in New Zealand are examples of transform faults. - Trench: A very deep valley in the ocean floor that marks where subduction of an oceanic plate occurs. Several people, geologists as well as others, have made observations that led them to wonder whether the continents had ever moved. Alfred Wegener put a large body of evidence together and formulated a theory called continental drift. Wegener gave the name Pangaea to the supercontinent he envisioned—from two Greek words meaning “all earth.” Because radiometric dating had not become a reliable part of the geological toolbox by 1915, Wegener would not have known how long ago Pangaea began to break up, but we now place it at about 200 million years ago. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

and then split in two as the seafloor spread away from the ridge. This solves the problem of how to get the continents to “drift” and opens up Wegener’s theory to examination again. As a complete side note (in other words, this won’t show up on the exam), mathematical models of a planetary magnetic field generated by convection currents in a molten iron core show that it is indeed possible to have a planet’s magnetic field spontaneously reverse itself. The reversal takes place over a fairly short (geologically speaking) period of time. A summary of the evidence for continental drift and seafloor spreading is shown in this video: Video 27.1. Continental Drift Wegener’s idea that continents drift over time was revamped and modified. Plate tectonics was the resulting model. Plate tectonics says that the surface of the Earth is broken into lithospheric plates. These plates rest or float on the mushy, semi-liquid, weak asthenosphere. The boundaries of the plates are marked by the earthquakes around the globe, as Activity 27.2 shows. Activity 27.2. Earthquakes and tectonic plates In case you were wondering where the tectonics part of the name “plate tectonics” came from, Tekton was the carpenter in the Iliad, so “tectonics” refers to building. The plates move anywhere from one centimeter each year (the African plate) to twelve centimeters each year (the Indian plate). These plates or “slabs” of the lithosphere are so massive that it’s sometimes hard to imagine anything that could move them. The plates move Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

form. This type of plate boundary is where continental accretion occurs. Continents are collections of smaller pieces that have been assembled through plate tectonic collisions over time. When continental collisions occur, the two slabs of continental lithosphere are “welded” or “sutured” together, resulting in a thickened section of lithosphere and a folded mountain belt. Eventually the mountains are worn away by erosion, but the continent is larger than it was before the collision. Continents grow by accretion as this process is repeated. The geologic ages of the rocks in any one block of accreted continental crust tend to be about the same, so we can recognize the boundaries of the accreted blocks by looking at the ages of the rocks. This map shows the blocks that constitute North America. Transform boundaries can also occur in either oceanic lithosphere or continental lithosphere. They are boundaries that connect other types of boundaries such as ridge-to-ridge, trench-to-trench, or ridge-to-trench. Transform boundaries occur when a plate slides sideways relative to its adjacent plate; they are most commonly found connecting different pieces of divergent plate boundaries, as Video 27.7 shows. Video 27.7. Transform Fault—San Andreas As you can see in the video, the plates are not converging or diverging relative to one another. Here are some of the transform faults that connect the Mid-Atlantic Ridge. Some transform faults, such as the San Andreas Fault, occur in continental lithosphere. The fault is obvious in photographs such as these. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

b) deep sea trenches c) island arcs d) volcanic activity 5) Which of the following are found at convergent plate boundaries involving continental crust on both plates? a) earthquakes b) fold mountain belts 6) Which of the following are found at transform boundaries? earthquakes 7) What type of plate boundary is represented by this area? oceanic-oceanic convergent zone 8) Which of the following types of landforms would you expect to find at this plate? Trench 9) What type of earthquakes would you expect to find here? frequent, severe, and varying in depth from shallow to deep 10) Based upon the geologic map, which plate is being subducted? The southeast side 11) This picture shows the plates in the northern hemisphere. The Mid-Atlantic Ridge runs down the middle of the Atlantic Ocean. What direction is the North American plate moving relative to the Eurasian plate? West 12) This is a map of the western part of North America. Some geologists believe that a continental rift zone is forming between Baja California and the rest of North America. If this rift zone were to continue, what would be the eventual result in this region and the Gulf of California? New ocean Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

the lithosphere. All of the plates have a mix of continental and oceanic crust on their surface, but what type of crust is present where two plates touch does make a difference in the features you'll see at that point. 1) What tectonic activity causes volcanic activity on Hawai'i? hot spot 2) How do you know what the plates are doing? What features are present? a) volcanic activity b) a nearly straight line of extinct volcanic islands with only one island at the end of the chain that has an active volcano c) shallow earthquakes that are nearly always weak 3) What type of plate boundary causes earthquakes in Japan? Ocean-ocean convergent 4) How do you know what the plates are doing? What features are present? a) volcanic activity b) an arc of volcanic islands where most of the islands have active volcanoes c) a deep ocean trench d) deep earthquakes that can be very strong e) shallow earthquakes that can be very strong 5) What tectonic activity causes volcanoes in Mexico and Guatemala? Ocean-continent convergent 6) How do you know what the plates are doing? What features are present? a) volcanic activity b) an arc of active volcanic mountains on the edge of a continent c) a deep ocean trench d) deep earthquakes that can be very strong e) shallow earthquakes that can be very strong 7) What tectonic activity causes the Earthquakes in Nepal? Continent-continent convergent 8) How do you know what the plates are doing? What features are present? a) A belt of mountains with few if any active volcanoes. b) Shallow earthquakes that can be very strong. 9) The evidence can get a little harder to decipher. You don't really need to be able to figure out the more complicated situations, so the next few questions are "zero points". They require looking beyond just the spot indicated to figure out what is going on. If you want a challenge here is the first. What causes the earthquakes in Puerto Rico (and Haiti)? a) ocean-continent convergent b) transform 10) What type of plate boundary causes earthquakes and volcanoes in New Zealand? a) ocean-continent convergent Explanation: Fun fact...while they'd known that New Zealand sat on an underwater plateau for quite a while, they didn't look closely at the rocks and figure out that it was a sunken continent until the last few decades. b) transform Explanation: There's a huge transform boundary connecting the converging plate boundary south of New Zealand to the one to the north that runs smack through the Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

south island. The answers to the questions 9 & 10 are: Haiti and Puerto Rico are on a transform boundary that borders a convergent boundary. There is an arc of volcanoes that make up the lesser Antilles, telling you that the Atlantic and Caribbean plates converge along there. So the greater Antilles (Cuba, Hispaniola, Puerto Rico) are on a transform boundary. New Zealand is on a large transform fault. But the pacific plate is also converging with a submerged continent (see Zealandia). So, you have volcanic activity from an ocean continent plate boundary. CHAPTER 28: GEOLOGIC TIME Introduction Ever heard the joke, “Why should you never lend money to a geologist when he promises to pay it back in a little while?” The answer, “Because ten thousand years is a little while to a geologist,” is something to keep in mind going into the start of this lesson. With a few exceptions, changes in the Earth occur very slowly. Geologists are used to dealing with the times necessary for these changes to take place. You can probably recall an earthquake or a volcanic eruption that occurred suddenly. Even though these may be devastating and receive a lot of attention, most of their effects are local and don’t cause change over large regions of the planet. On the other hand, when you look at layers of sedimentary rock on a mountainside or in a road cut, you are looking at a process that must have taken a very long time if depositing that much sediment occurred in the past at roughly the same rates it occurs today. Most of the geologic processes that we have covered in the past lesson and will cover in the following chapters also occur slowly. The measurement of time, therefore, becomes crucial for gaining an understanding of the way in which our planet has arrived at its present condition and for predicting what might happen in the future. Key Terms - Cross-cutting: Rock that is cut is older than the other rock, fault, crack, and so forth, that did the cutting. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

- Faunal succession: Fossil assemblages (groups) found in sedimentary rocks are diagnostic of rock age. Extinct assemblages never appear in younger rock. - Inclusions: Rock that is included (surrounded by) other rock must be older than the surrounding rock. - Original horizontality: Rocks are deposited in horizontal layers. Any tilting, folding, or other deformations occurred after the initial deposition. - Superposition: The rocks on the bottom are older than the rocks on the top (unless the rock units have been overturned completely). Just as Newton’s laws and conservation laws are major tools for a physicist, and a chemist is always turning to the periodic table and the quantum model, the principles of relative dating are some of the basic and most-used tools of a geologist. These five principles are summarized below with a little explanation. Think about them in terms of cause and effect (remember the good old principle of causality?), and they should make sense. 1) Original horizontality - Rocks are deposited in horizontal layers. Any tilting, folding, or other deformations occurred after the initial deposition. 2) Superposition - The rocks on the bottom are older than the rocks on the top (unless the rock units have been overturned completely). The bottom layers were deposited, and then the next layers were deposited on top of them. Note that this doesn’t mean the deposition of the sediment has been continuous. There might have been layers that have been eroded away. 3) Cross-cutting - Rock that is cut is older than the other rock, fault, crack, and so forth, that did the cutting. The cut rock had to exist first in order to be cut. 4) Inclusions - Rock that is included (surrounded) by other rock must be older than the surrounding rock. 5) Faunal succession - Fossil assemblages (groups) found in sedimentary rocks are diagnostic of rock age. Extinct assemblages never appear in younger rock. Basic Examples Using these principles, it is possible to decipher the sequence of geologic events. None of the principles provide direct evidence for the age of anything, but they allow the order of events to be worked out. Sometimes the sequence of events can be fairly straightforward, and sometimes it can be pretty tricky—kind of like the range that exists with sudoku or crossword puzzles. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

1) Order the different rock types from oldest (first line) to youngest (last line). C,B,A 2) Which principle of relative dating was used to provide the correct relative dates of these sedimentary layers? superposition Use the following information to answer the next 2 questions: This picture shows two different rock types, A and B. 3) Which type of rock is older? rock A 4) Which principle of relative dating was used to provide the correct relative dates of these rocks? cross-cutting Use the following information to answer the next 5 questions: This picture shows three different types of rocks: A, B, and C. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

5) Which principle of relative dating can be used to provide the relative dates of rocks A and C? inclusion 6) Between rocks A and C, which rock type is older? rock A 7) Which principle of relative dating can be used to provide the relative dates of rocks A and C (considered together) versus rock B? cross-cutting 8) Which rock type is older between rocks A and C (considered together) and rock B? rocks A and C 9) Order the different rock types from oldest (first line) to youngest (last line). A,C,B We haven’t included exercises for the principle of faunal succession because it does not lend itself as well to the use of photographs. Those who study fossils for use in relative dating (or for a host of other reasons) are called paleontologists. Oftentimes they must examine minute details of a fossil to determine its species and the time period during which it lived. We aren’t going to become experts in fossil identification in this course, but we can illustrate the principle of faunal succession with a schematic exercise. Use this diagram to test your basic knowledge of how faunal succession works. You find a layer of rock that contains these two fossils: Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

10) What interval of time, as indicated by the numbers at the right side of Figure 28.4, is represented by the simultaneous existence of these two animals? intervals 3 & 4 Using faunal succession often requires a level of expertise that only specialists will attain. However, the other principles require nothing more than basic knowledge of how rocks form, common sense, and perhaps some good observation skills. Your textbook has a good example of the geologic history of the Grand Canyon. Let’s try out two more examples where we can use a variety of relative dating principles to determine a geologic history of the area. Example 1: Siccar Point, Scotland These pictures show the geology at Siccar Point in Scotland. This is the place that inspired James Hutton to contemplate the immensity of geologic time. Figure 28.6 shows layers A truncating or cutting off layers B. Figure 28.7 shows what appear to be inclusions of B in A. In Activity 28.1, drag the events on the left into the boxes on the right so that they are in chronological order. Siccar Point Sequence First - Deposition of B Second - Deformation (tilting) of B Third - Erosion of B Fourth - Deposition of A Fifth - Deformation (tilting) of A Sixth - Erosion of A Notice that erosion has played a big role in shaping what we see. Rock B was deposited and tilted, and then it was eroded. This erosion acts like an eraser of our knowledge of what Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

happened in geologic history. This erasing or deleting of geologic history is known as an unconformity . An unconformity is a gap in the geologic record. Were there layers that formed after Rock B but before Rock A that were eroded away? Because pieces of Rock B are found in Rock A, probably not, but other unconformities in other areas can leave much bigger gaps in the geologic record. When a geologist encounters an unconformity, it can be an exciting and frustrating experience: “Wow! Something happened here! But what?!” Then, he or she must use principles of relative dating and clues from the surrounding areas to try to piece together what happened. Depending on how large the unconformity is (in terms of time as well as area affected), it can be easy or hard to determine what happened. The activity below shows Siccar Point with a yellow line that traces the unconformity in the rocks. 11) Of the following, which of the relative dating principles did you use? (Select all that apply.) a) cross-cutting b) original horizontally c) inclusions Example 2: The Moon Use the following information to answer the next 8 questions This picture shows features on our moon. 12) Compare the craters marked A with the lava plain marked C. Which is older, A or C? C 13) Which principle of relative dating did you use? cross-cutting 14) Now compare the craters marked A with the crater whose wall is marked by B. Which is older, A or B? B 15) Which principle of relative dating did you use? cross-cutting Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

16) Compare the rays of ejected material marked D (from a crater just off the bottom of the picture) with the lava plain marked C. Which is older, C or D? C 17) Which principle of relative dating did you use? superposition 18) Which of the following is the oldest feature marked in the photograph? C 19) Of the two craters marked in the orange square in the lower right corner, which is the youngest? the lower right crater By the early part of the twentieth century, radioactive decay was understood well enough that it was being used for the first measurements of the absolute ages of rocks. As many scientists suspected, many rocks turned out to be pretty old. Radiometric dating is based on the assumption that the half-lives of radioactive isotopes do not change with time. If the amount of undecayed radioactive isotope of some element in a rock can be determined, along with the amount of its daughter product (the isotope the radioactive isotope decays into), then in principle the age of the rock can be calculated. We aren’t really going to talk much about the methods by which the amounts of parent and daughter isotopes in a rock are determined for radiometric dating. Your textbook discusses them a little. The methods involve meticulous and sometimes tedious laboratory procedures as well as some corrections for things such as the amount of daughter isotope that was originally in the rock, but they are done routinely. Once the amounts of remaining parent and daughter isotopes in the rock are known, a decay curve can be used to determine the age of the rock. 20) Suppose you have a rock sample containing uranium, some of which is 235U, which decays to 207Pb with a half-life of 713 million years. You find that only 25% of the original 235U is still present, the rest having decayed to 207Pb. What can you determine about the age of the rock? The rock is 1.4 billion years old So what does the “age” of a rock mean? Well, that depends. If the rock is igneous, then the age is the time since the mineral in the rock solidified from molten material. At that point, there was either no daughter product present (as in the case of argon, because argon is a noble gas and would not be present in a rock unless from the decay of potassium), or we can correct for how much there was (as in the case of lead that did not come from the decay of uranium after the rock formed). If the rock is metamorphic, then it has been significantly heated during its history, and, for many types of radiometric dating, that has reset the decay clocks. This means a radiometric date from a metamorphic rock usually gives us the time since its most recent heating. While this isn’t exactly what you might think of as “age,” it may be very useful information to a geologist trying to unravel a piece of geologic history. If the rock is sedimentary, the minerals of which it is made may have come from several different (and generally unknown) sources. This means the ages obtained from different grains pertain not to the formation of the sedimentary rock but to the preexisting rocks from which the sediment was eroded. Therefore, radiometric dates are generally not very useful for sedimentary rocks. Often geologists can use radiometric dating as well as relative dating techniques, as Figure 28.9 illustrates. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

21) In this picture, A and B are igneous and are 33 and 21 million years old, respectively. C is sedimentary rock. What is the age of this sedimentary layer? older than 33 million years Earth is obviously older than the oldest rocks found on it. These rocks are between 3.8 and 3.9 billion years old. There are minerals found in sedimentary rocks that are about 4.2 billion years old, but the sedimentary rocks themselves are younger, of course. Earth must therefore be older than 4.2 billion years. How much older? According to our best theory, the nebular hypothesis (which we will study in Lesson 32), the currently accepted model for solar system formation, meteorites, and the Moon should be the same age as the Earth. The oldest meteorites and the oldest moon rocks both date to around 4.6 billion years. So we take that as the age of the Earth. One Final Example Use the following information to answer the next 9 questions: Earth is obviously older than the oldest rocks found on it. These rocks are between 3.8 and 3.9 billion years old. There are minerals found in sedimentary rocks that are about 4.2 billion years old, but the sedimentary rocks themselves are younger, of course. Earth must therefore be older than 4.2 billion years. How much older? According to our best theory, the nebular hypothesis (which we will study in Lesson 32), the currently accepted model for solar system formation, meteorites, and the Moon should be the same age as the Earth. The oldest meteorites and the oldest moon rocks both date to around 4.6 billion years. So we take that as the age of the Earth. Consider the features shown in the photograph: 22) The gray igneous rock is younger than the red sandstone. 23) Which principle of relative dating did you use to obtain your answer? cross-cutting 24) Where are the youngest visible beds of sandstone located in this photograph? at the top 25) Which principle of relative dating did you use to obtain your answer? superposition 26) Could the igneous rock be successfully dated by radiometric means? YES Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

27) Could the sedimentary rock be successfully dated by radiometric means? NO 28) Could either the sandstone or the igneous rock be a candidate for the oldest rock on the earth? No, the sandstone consists of fragments eroded from rocks that are older than it is, and the igneous rock is younger than the sandstone 29) If the igneous rock is dated to be 34 million years old, what principle of relative dating was used to get this result? none—that’s an absolute date 30) If the igneous rock is dated to be 34 million years old, what happened 34 million years ago? The lava solidified Chapter 28 Quiz 1) This picture shows three different types of rocks, A, B, and C. Which principle of relative dating can be used to provide the relative dates of rocks A and C? Inclusion 2) In this picture, A is a rock radiometrically dated at 37 million years, and B is also a rock. (Note: The age of 37 million years has been used for purposes of this question only. The actual age of “A” is not really 37 million years.) Using cross-cutting relationships, we know that B is younger than 37 million years 3) In this picture, A is a cinder cone (a type of volcano) and the dark rock nearby with the arrow pointing to it is lava from the volcano. B and C are sedimentary rocks and D is igneous. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Which of the following lists the age of the rocks from oldest to youngest (oldest first)? C,B,D 4) Uniformitarianism says that the same geologic processes occurring today in a particular location on Earth occurred in the same places in the past. False 5) To be useful as a geologic clock, which of the following conditions must be true for a radioactive isotope? The isotope must be fairly common and have a long half-life 6) Look at this diagram. Which of the following lists is ordered from oldest to youngest? (Note: C refers to the fault.) B,C,A 7) Look at this diagram. Which of the following lists has the rocks ordered from oldest to youngest? (Note: E is a fault, not a rock.) B,A,D,C Chapter 28 Homework 1) Below is a geologic cross section of the Grand Canyon. Different rock layers are labeled. What does the contact between layer 3a and the layers below (group 1 & 2) represent? Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

a) An unconfomity b) An erosional surface where many rock layers have been lost. c) A large gap in time in the geologic record. In the cross section below, rock J and L are igneous rock. N and K are faults. H and I are metamorphic rock. The other layers are sedimentary rock. After you've come up with your own series of events, click on the link below the picture to see a video breakdown of what might have happened to create the cross-section. 2) When you compare the ages of layers A-I, what principle do you use so you know what order to put them in? Superposition 3) When you compare the ages of items J-N, what principle(s) do you use so that you know what order to put them in? Cross-cutting 4) Put items D, K, & L in the correct order oldest to youngest. Type them in the box below. LDK 5) Which layers could you date by measuring absolute ages for the rock? Just the igneous layers 6) Lava from volcanic eruption J created a vein off to the right that didn't ever break the surface. Because it was underground, it would have cooled and solidified much slower than material that erupted onto the surface. If you were to radiometrically date lava from the surface and lava from this underground vein what would you expect to find. If the underground vein originated from the same eruption, it will date younger than the rocks on the surface. CHAPTER 29: EARTH MATERIALS Introduction Throughout this course, we have classified and categorized various phenomena, ranging from the properties associated with waves and with particles to the types of chemical bonds. In geology, there are also basic classifications that help a geologist make more sense of the rocks being studied. One of the basic classifications has to do with the types of rocks that exist. The three categories of rocks are igneous, sedimentary, and metamorphic. Within these rock categories are large differences in appearance and behavior, but all these rocks have one thing in common—minerals. Previously, we briefly discussed minerals in terms of their properties due to the arrangement of the elements in the mineral. In this lesson, we will briefly revisit the idea of minerals. Then we will discuss the three rock types and study how these rocks form. Key Terms Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

- Precipitate: A solid formed inside a liquid by a chemical reaction. - Igneous rock: The type of rock formed when melted material (magma) solidifies. - Sedimentary rock: The type of rock created from sediments weathered from other preexisting rocks. - Metamorphic rock: The type of rock created when preexisting rocks are altered by heat and pressure but are not melted. - Dissolution: To break apart or dissolve in a solution (liquid). - Physical weathering: The breaking down of rocks through physical processes such as freezing and thawing. - Chemical weathering: The breaking down of rocks through chemical processes such as acidic reactions. - Plutonic: Pertaining to igneous rocks formed under the surface of the earth. Igneous rocks formed in this manner typically have larger mineral sizes due to the longer cooling times. - Volcanic: Pertaining to igneous rocks formed at the surface of the earth. Igneous rocks formed in this manner typically have smaller mineral sizes due to the short cooling times. - Clast: A grain of rock weathered from an existing rock. - Hydrothermal circulation: Movement or circulation of hot water. - Hydrolysis: A type of chemical weathering in which water interacts with the minerals in the rock to form new minerals and leave ions in the water. Silicate-rich rocks and carbonate-rich rocks often experience this type of chemical weathering. - Oxidation: A type of chemical weathering in which water interacts with the minerals in the rock to form new minerals and leave ions in the water. Metal-rich rocks often experience this type of chemical weathering. Minerals are the building blocks of rocks. There are many different types of minerals, and they all meet the following criteria. A mineral: - is naturally occurring - is an inorganic solid - has a fixed or narrowly limited chemical composition - has a definite internal crystal structure - has a unique set of physical properties - has some stability in the face of varying pressure, temperature, or in the presence of water - The images in the table below show some common (and not-so-common) minerals. Notice the shape of the crystals. This shape is from the internal crystal structure and chemical composition, as we have already discussed in Lessons 22 and 24. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

All rocks are made up of minerals, some are common such as quartz, potassium feldspar, hornblende, and diopside. Some are less common such as gold and diamond. 1) The surface of Pluto is over 90% solid nitrogen. This means that Nitrogen is a mineral. TRUE For a quick overview of the rock cycle, watch this video. PHY S 100 Chapter 29 | Earth Materials Many rocks do not form at the surface of the earth (volcanic rocks excepted) but are Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

eventually exposed there by erosion. Igneous rocks crystallize from magma. Sedimentary rocks form in layers. As sediment is deposited in the form of eroded debris of other rocks, chemical precipitates (solid chemicals that form out of liquids, such as ground water), or organic material, the layers on the bottom are compressed, and the particles are cemented together into rock by minerals found in the groundwater. If rocks are buried deeply enough and subjected to high temperatures (without melting) and pressures, chemical reactions may take place that alter the rock into something recognizably different from what it was. These are metamorphic rocks. An igneous rock can be weathered away, and the clasts (weathered rock grains and chunks) can form a sedimentary rock such as a sandstone, as this picture shows. An igneous rock can also be subjected to heat and pressure, and metamorphism occurs to form a metamorphic rock. This gneiss is an example of a metamorphic rock where granite was the protolith, the original rock before metamorphism changed it into gneiss. As this diagram of the rock cycle shows, sedimentary rocks can experience metamorphism or erosion to form metamorphic or sedimentary rocks as well. The same process can occur with metamorphic rocks. 2) Which of the following best represents the rock cycle? a) Igneous rocks erode into sediment. Sedimentary rocks get buried and turned into metamorphic rock. Metamorphic rock melts and turns back into igneous rock. b) Metamorphic rock erodes into sediment Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Rocks fall into three primary types—as you’ve already guessed from the previous information. Igneous Rocks As we mentioned before, igneous rocks form from magma. If the rocks cool below the surface of Earth, the igneous rock is called a plutonic rock. Because it is below ground, the cooling time is much longer. This additional time allows larger minerals to form. Granite, diorite, and gabbro are examples of plutonic rocks. When the cooling takes place above the ground, the igneous rock is termed a volcanic rock . Because the rock cools quickly as it hits the much cooler air or water, the minerals are much smaller—often microscopic. Basalt, pumice, and obsidian are examples of volcanic rocks. In fact, pumice and obsidian cool so quickly that they are called glassy volcanic rocks—minerals did not have time to form at all in pumice and obsidian. Each of the plutonic rocks shown above has a volcanic analog. The rocks shown in the table below have the exact same mineral composition as granite, diorite and gabbro respectively. They just cooled much more quickly. - Granite - Diorite - Gabbro - Rhyolite - Andesite - Basalt Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Because granite and basalt are the most common rocks on continents and in ocean basins, respectively, you do need to know those two rock names. Don’t worry about memorizing any other igneous rock names unless you just love rocks—if you do, I get it! I love rocks too! Just remember what a rock’s color and crystal size tell you about where and how they formed and why the color and crystal size tell you this. At places such as convergent plate boundaries, where an oceanic plate is subducted, water can be added to overlying rock through the heating of water-bearing minerals. These water-bearing minerals were formed earlier at mid-oceanic ridges by hydrothermal circulation. The addition of water is significant. This water, released as the minerals melt and break down, changes the chemical makeup of the overlying rock. It allows the rock to melt at a lower temperature. Nearly all materials are less dense as liquids than solids, so it becomes more buoyant. As this occurs, the resulting magma begins to rise. As the rock rises, the pressure on the rock drops. A drop in pressure further lowers the melting temperature of the minerals, and more material melts. If the magma does not rise to the surface, plutonic rocks are formed. An ascent to the surface creates volcanic rocks. 3) A solid rock near the melting point that contains no water is located below a divergent plate boundary. As the lithosphere above it moves apart, the pressure on the rock is reduced. What will happen? When the pressure drops, the rock will start to melt. 4) At subduction zones, rocks are "hydrated" when the original minerals combine with the water present in the subducted ocean plate to form new minerals. What will happen to a solid rock that was near its melting point once it has been chemically combined with water (hydrated)? The hydrated minerals will melt Sedimentary Rocks Figure 29.10 and figure 20.11 show two examples of an environment where sedimentary rocks are being created. In these environments, sediment is being deposited. There are two ways that the sediment that makes up sedimentary rocks can form: physical weathering and chemical weathering. Most physical weathering occurs due to water. Flowing water can erode rocks and sediment. In areas where the water freezes, the water will enter cracks and crevices. When the water freezes, it expands, which exerts a large contact force on the rock. Over time, this freezing and subsequent thawing causes the rock to break into pieces, as seen in the figure below. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

This is part of the reason why, in Utah at least, it is said there are only two real seasons: winter and construction. Once these pieces are created, water can move the smaller clasts elsewhere where they can be deposited to form sedimentary rocks, as shown in the river floodplain in figure 29.11. Chemical weathering occurs when water, which is often somewhat acidic, dissolves the rock. When this dissolution occurs, the water now has dissolved elements in it derived from the rock. These elements in the water can form new sedimentary rocks. There are other types of chemical weathering besides dissolution. In these weathering reactions, the formation of a new mineral occurs as well as the release of ions to the water. This is where clay minerals come from, for example. Finally, biological activity can also help create sedimentary rocks. Organisms making CaCO3 are responsible for making most limestone. Limestone and rock salt are examples of sedimentary rocks formed by chemical precipitation. Figure 29.10 previously showed an environment where limestone was being created. Gypsum (used in wallboard) is a mineral formed by chemical precipitation and can be found in rocks. Because I love rocks and maybe you do, too, I thought I’d share an amazing photograph of the Cave of Crystals in Mexico where huge gypsum crystals are found. Look at the person in the lower right hand corner to get an idea of the size of these amazing and rare (size-wise) crystals. The elements and ions in the water can also precipitate (be deposited in solid form) to Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

form the cement between the clasts formed by physical weathering. Additional examples of sedimentary rocks are sandstone, conglomerate, and shale, as shown in the pictures below. Metamorphic Rocks No, there is not a problem with the image loading. Metamorphic rocks form deep within Earth’s crust, often along the contact between a body of magma and the surrounding rock and also at convergent plate boundaries. At these locations, which we can’t see, there is enough heat and pressure to create the intense temperatures and pressures needed to cause the minerals in the rock to change, to lower its energy and/or increase its entropy. Then, other tectonic forces cause the metamorphic rocks to be raised and subsequently exposed by erosion. Because gravity pulls down, not sideways, or plate collisions occur in a certain direction, the pressure typically comes from one direction rather than being uniform in all directions. This often leads to stripes and layers, called foliation , forming in the rock. While foliation occurs in many metamorphic rocks, not all metamorphic rocks exhibit this layering or banding. Marble, shown below, is an example of a metamorphic rock that often doesn’t have foliation. It is called a nonfoliated rock. Other metamorphic rocks, such as gneiss, are foliated. Using foliation, it is possible to determine the direction of the unbalanced force on the rock. As the figure below demonstrates, an unbalanced force due to the pressure causing the metamorphism is placed upon the rock. The minerals are “squished” to the side due to this force. This squishing causes the foliation, and the foliation is perpendicular to the applied force. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Other examples of metamorphic rocks are shown below. Can you identify the foliated rocks from the nonfoliated rocks? 5) Which of these rocks are not foliated? quartzite This diagram below depicts a hypothetical cross-section of part of the Earth w/ igneous, sedimentary, & metamorphic rocks. See if you can determine whether the rock layer is igneous, sedimentary, or metamorphic. Then click on the numbered buttons to check your answers. What principle tells you that the magenta rock is older than either the light greenish- yellow or dark purple rocks? Did you use more than one principle? Chapter 29 Quiz 1) B ased on these photos of igneous rocks, which of them cooled quickly above Earth’s surface? Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

2) Which of the following forces applies to the movement of a magma body? buoyant force and gravity 3) This is a picture of a metaconglomerate, which resulted from a sedimentary rock called conglomerate rock experiencing high pressure and temperature. The clast that made up the conglomerate rock was much more spherical. Now look at the clasts whose shapes have been altered due to metamorphism. Based upon what you know about foliation, which of the following arrows best describes the direction of the pressure on the conglomerate as it was experiencing metamorphism? Hint: Look at the way the clast is squished from being non circular. What direction of force would allow this change in shape? Arrows above 4) A sinkhole, like this one, can form in limestone when water dissolves it. Which of the following best describes this type of weathering? chemical weathering 5) Here is a photograph of a talus pile on the front of Mt. Timpanogos in Utah. Which of the following best describes the weathering process which created this pile? physical weathering 6) This picture shows a siltstone, which is a clastic sedimentary rock. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Which of the following best describes how the siltstone is cemented together? The siltstone clasts are held together by minerals precipitated by ground water Chapter 29 Homework Compare and contrast the following pairs of rocks. Explain how the pairs of rocks are related to each other. What is the same; what is different and why? a) Granite and Rhyolite - compare: They have very similar compositions, as they are both composed of quartz and feldspar. - contrast: Granite is plutonic and crystallizes at depth, whereas rhyolite is volcanic and is erupted onto Earth's surface. Also, granite is composed of plagioclase and crystals of granite can be easily seen. However, rhyolite is composed of biotite & pyroxene and cannot be seen without a microscope. b) Rhyolite and Basalt - compare: Both are types of igneous rocks and are both extrusive rocks based on the method of formation. Extrusive rocks means that very hot magma which is inside the earth, extrudes (or flows out) onto earth's surface in the form of lava. - contrast: Rhyolite is light in color and is a sticky lava that usually does not flow very far from the place where it erupts. In addition it is formed from magma which is rich in silica. Basalt is a volcanic rock that is usually a black or dark brown color. Basalt is also formed from lava and it contains an abundant amount of iron and magnesium but contains little silica. c) Granite and granitic gneiss - compare: Both granite and granitic gneiss are made of feldspars, quartz, mica, and smaller amounts of dark colored minerals such as hornblende. In addition, they both have tightly interlocking minerals, so they are minimally porous, and they have similar properties and can be used in the same ways. - contrast: Although they are both related, granite is an igneous rock and granite gneisses are formed from the metamorphism of such igneous rock at hight temperature and pressure. d) Limestone and marble - compare: Their chemical nature is very similar to each other, as both limestone and marble are types of rock made of calcium carbonate residues. - contrast: There are many differences in the way they originate and the physical characteristics they possess. Limestone is a sedimentary rock, and is lighter in density. Marble, however, is a metamorphic rock and is heavier in density. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

CHAPTER 30: SURFACE PROCESSES Introduction When I was a young child, my family would embark on epic cross-country journeys. My dad was a teacher and thought that summers were made for car trips. The trips were long, and after a while, coloring books, singing songs, and reading in the car began to get old. There were no TVs in cars back then, so partly in desperation brought on by boredom and partly because the land was so amazing, we would begin to guess how certain features in the landscape had formed. Looking back, our guesses were pretty far off—a huge dinosaur wasn’t suddenly covered in mud to form a weird-shaped hill, for example. As small children, we knew about streams, but we didn’t realize the importance they played in shaping the landscape. Streams are part of the hydrologic system which, along with the plate tectonic system, shapes the surface of the Earth. As we discussed in Lesson 27, the plate tectonic system plays a major role in determining the locations of mountain ranges, volcanism, earthquakes, and so forth. However, it is the hydrologic system that gives distinctive form and detail to the surface of Earth. It does this through both erosion and deposition. In this lesson we will discuss the effect of the hydrologic system on the earth. Key Terms - Alluvial fan: Sediment and debris at the mouth of a canyon deposited by intermittent water flow. - Alpine glacier: A glacier formed in a mountain valley. - Base level: The elevation of a stream’s end point. - Cone of depression: A region next to a well or source of groundwater discharge where the water table is lowered. - Continental glacier: A glacier covering a large portion of a continent or land mass. - Delta: Sediment and debris deposited in an ocean or lake at the mouth of a river. - Downcutting: The erosion of the base of a stream until the stream reaches its equilibrium profile. - Equilibrium profile: The slope of a stream at which sediment is transported instead of deposited and eroded. - Flood plain: Plains intermittently covered with water from a flooding river. - Hydrological cycle: The movement of the various reservoirs on or near Earth’s surface. - Moraine: Rock and sediment carried by a glacier. - Permeability: A measure of how easily water can flow through rock or sediment. - Porosity: The percentage of empty spaces in a rock or the percentage of space in a rock that water can occupy. - Reservoir: A place or state where water can reside within the hydrological system. - Slope retreat: The erosion of the sides of a stream. - Stream: A conduit through which surface water moves, either constantly or intermittently. This can be a large river such as the Nile, Amazon, or Mississippi; a smaller river such as the Provo or American Fork; a creek; or even a stream formed by a flash flood in the Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

desert. - Water table: The depth in the ground where rock is saturated with water. You are probably fairly familiar with most of the components of the hydrologic system, although you may think that it involves only water. Remember way back to Lesson 6—fluids include both liquids and gases. That means we consider the air that moves over the Earth’s surface to be part of the hydrologic system, especially since it contains water vapor. In addition, even though the ice of glaciers may not seem much like a fluid, we include it because it results from precipitation. Glaciers also flow to take the shapes of their “containers,” so they behave as fluids as well. The hydrologic system also affects deserts. Even under the most arid deserts, there is groundwater at some depth. This is the water that fills the pore spaces in the rocks or loose sediment beneath the earth’s surface, and it is part of the system too. That leaves only streams (running water) and the reservoirs of standing water such as oceans and lakes to complete the hydrologic system. The fluids in the hydrologic system are not static. They move constantly, and there is a general systematic trend in their motions. Again, thinking back to Lesson 6 and even Lesson 27, recall that fluids denser than their surroundings sink while those less dense rise. This results in convection currents. As water evaporates to water vapor, convection currents in the atmosphere move it, and as it cools, it condenses to liquid or solid water, which then falls to the surface as rain and snow. The following animation demonstrates this cycle known as the hydrological cycle. NASA: The Water Cycle Now let’s look at parts of the hydrologic system that have the greatest effect on Earth’s surface. These are streams, ice, and groundwater. Notice that I haven’t included wind and oceans or lakes. While wind and reservoirs such as oceans and lakes certainly affect the earth, their consequences—erosion and deposition—are more limited to very arid areas (for wind) or near the shorelines (for oceans and lakes). 1) Water that evaporates from the ocean precipitates back into the ocean and water that evaporates over land precipitates over land. FALSE Use the following information to answer the next 4 questions: The erosional and depositional effects of streams are seen nearly everywhere on the land surface of Earth. Erosion by streams is the most effective agent in lowering the elevations Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

of the continents over long time periods, and the effects of stream erosion can be seen almost everywhere. Think of the driest desert you can imagine. Hot . . . arid . . . hostile to plant and animal life. Got it? Okay, maybe you are thinking of something like the Rub al-Khali, a great sea of sand on the Arabian Peninsula, known as the “Empty Quarter.” This satellite image shows the edge of that great desert in the Republic of Yemen. Now, what might have caused this branch-like pattern of dry gullies? I hope you said “running water,” because it was running water that flowed through those channels. After the last ice age, when the climate in this part of the world was more moderate, the area hosted grasslands. Also, although infrequent, flash floods have moved large amounts of sediment through all those gullies over time. Before proceeding, remember from your reading of the textbook that geologists call any confined body of running water a stream, even if you might call a large one a river and a small one a creek. Using the term stream constantly avoids having to worry about the size. We also call watercourses that carry water only during flash floods intermittent streams . So those are streams too. Humans have long been dependent on stream systems as sources of water. As this video discusses, understanding how they function is important so that we can avoid problems when we use these resources. PHY S 100 Chapter 30 | Surface Processes Stream Erosion and Stream Deposition If you look at a single stream tributary and its main stream, the two almost always meet at the same elevation. This is very strong evidence that the streams have carved their valleys— that is, the water does not just happen to occupy the topographically low places—but instead, the streams have eroded the land to create the low places. This erosion occurs in two ways: downcutting and slope retreat. Streams erode the land because they carry material such as sand and pebbles that wear away at the sides and bottom of stream channels during periods of rapid water flow. Downcutting is accelerated when the base level of the stream is dropped. This causes the stream to no longer be at its equilibrium profile, and erosion occurs to achieve a new equilibrium. Your textbook explains different ways to change a stream’s base level, and one is to raise the land the stream flows over. That is what happened to the Colorado River and the land in the western United States. The Grand Canyon was the result. The region known as the Colorado Plateau experienced tectonic uplift, and the Colorado River cut the Grand Canyon in a manner similar to the way one applies pressure on a slab of wood when using a table saw. The following video shows how the Grand Canyon was able to be cut so deep and also what caused it to be so wide. The Grand Canyon: How It Formed Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

In any given stream channel, deposition and erosion may occur at different places at the same time. Deposition and erosion may also occur in the same places at different times. Let’s look at an example. The picture below is a photograph of a stream in the Grand Teton National Park. Notice the flat terraces at the sides of the river. These flat terraces are evidence that the stream has eroded into material that it formerly deposited in the same place. At one point, the upper terrace (indicated by the red arrow) was deposited, then partially eroded away, and then the second terrace (indicated by the blue arrow) was deposited and partially eroded as well. Erosion through sediment can take place much more quickly than erosion through bedrock, but the peaks and valleys in the background are testimony that solid rock can be eroded over time. Now look at the satellite picture of a winding (we call that meandering) stream in Peru, the Ucayali River. (Okay, we do use the term river if it is the proper name of a stream— Mississippi River, Nile River, and so forth.) In the next photograph, depicting the Yamal Peninsula in Russia, notice how many isolated curved lakes, called oxbow lakes, there are. These lakes are evidence that the stream has shifted around, eroding into its own deposited sediment. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Now, can you imagine how water moves along a meandering stream channel? Try predicting whether the most erosion will occur on the outside or the inside of the bends, as well as where the most deposition occurs, by answering the following questions. The video below shows a stream table that recreates this situation in a more accessible environment. Stream Table Meander Bend Run 2) Where does the water in the stream bend travel the fastest? The outside of the bend 3) What happens to the sediment in the stream as the speed of the water decreases? Sediment is dropped from the stream 4) Where does the most erosion take place in a stream bend and why? The most erosion takes place at the outside of the bend because water traveling on the outside of the bend must speed up due to the bend, so it can carry more sediment and therefore picks up sediment from the side. 5) Where does the most deposition take place in a stream bend and why? The most deposition takes place at the inside of the bend because water traveling on the inside of the bend must slow down due to the bend, so it cannot carry as much sediment and therefore drops the sediment in the bend. Use the following information to answer the next 2 questions: The deposition and erosion which occurs in a stream bend can be seen more closely in the picture below. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Stream Deposition Features Streams eventually carry their sediment to wherever they end (that is, base level) and deposit it. When the end of the stream is at a body of water like the ocean or a lake, the deposit of sediment is called a delta . As the stream empties into the ocean or lake or larger stream, the speed of the water slows and much of the sediment the stream was carrying is dropped to form the delta. As mentioned in the textbook, the reason it is called a delta is that sometimes it resembles an uppercase Greek letter delta, Δ. The images below show 2 different deltas. The Nile Delta is on the left & the Mississippi Delta is on the right. As you look at the two different deltas, answer the following questions: 6) Which of the two deltas looks most like the Greek letter delta? Nile Delta Explanation: The Nile Delta is shown in green due to the vegetation growing on the delta. 7) The Mississippi River deposits its sediment into quieter waters. How can you determine this from the two pictures shown? Strong currents in the Mediterranean Sea sweep sediment away from the Nile Delta. The Mississippi deposits its sediment into the relatively calmer water of the Gulf of Mexico and so is able to build its delta out and extend its channel. Explanation: The Nile Delta is able to form but is truncated, while the Mississippi Delta is not truncated. What could cut off part of the Nile Delta? This looks like a delta, but with one significant difference—instead of deposition occurring underwater as it does with a delta, the deposition occurs on the valley floor. To distinguish this from a delta, which by definition is a deposit in a body of water, we call this an Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

alluvial fan . Alluvium is a general word for material that is stream-deposited. You can see alluvial fans a lot in parts of the world that are both mountainous and arid, such as much of the American West. A floodplain (Figure 30.10), is also an example of a situation where a stream deposits sediment. When flooding occurs, the stream spreads out, overflowing its regular bed. As the stream spreads out, the water slows, thus losing energy. Sediment is dropped from the stream. All these work together to shape river and stream systems. In the video below, you can watch how they evolve through time on a stream table as we simulate seasonal flooding along with changes in base level. Glaciers can be classified as either alpine glaciers or continental glaciers. Alpine glaciers occupy valleys initially carved by streams. Continental glaciers are sheets of ice that cover very large areas. Both are very effective at shaping landscapes, but they are not as geographically widespread as streams. These two pictures show an alpine glacier and a continental glacier, respectively. Look at these two pictures. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

8) Which of the two valleys was eroded by an alpine glacier? Valley 1 Explanation: Look for the valley that is more U-shaped in its profile. 9) Where does a stream move the fastest? in the middle Use the following information to answer the next 2 questions: Alpine glaciers “scoop out” the valleys they occupy to make them U-shaped. Because a glacier is made of ice, the ice can just pick up sediment of all sizes. This sediment scours the sides of the valleys to the U-shape. Now contrast this U-shaped valley formed by an alpine glacier with the V-shaped valley formed by a stream. Can you explain why a river valley would be V-shaped? 10) Where will the stream remove the most material? In other words, where will the most erosion take place? in the middle Explanation: A higher stream speed allows more sediment to be carried and, therefore, more erosion to take place. Use the following information to answer the next question: In general, the stream flows the fastest in the middle of the stream. Here the water has the most kinetic energy and is able to carry the most sediment. This means that the most downcutting occurs in the center. In fact, as we discussed in the section above, deposition can often occur at the sides of the stream. In heavily glaciated mountains, the adjacent U-shaped valleys meet in sharp, angular ridges, as in this photo of the Baltoro Glacier in the Gilgit-Baltistan region of Pakistan. Alpine glaciers tend to produce very angular, sharp, and abrupt topography, but what about continental glaciers? An alpine glacier picks up sediment of all sizes, and a continental glacier follows the same pattern. Large boulders can be carried along with the ice leaving characteristic erosion streaks behind when the glacier finally melts. It is these streaks that Wegener and others used as evidence to support the idea of continental drift and plate tectonics Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

that we discussed in Lesson 27. The two pictures below show erosion streaks on the Yale Glacier, an alpine glacier in Alaska, as well as erosion streaks in Kelleys Island, Ohio, left by a continental glacier that covered much of northeastern North America 11,000 years ago. A glacier will both erode and deposit sediment just as streams do. We have just discussed erosion by alpine glaciers and continental glaciers, but both types of glaciers deposit sediment in ridges called moraines . Moraines are characterized by angular and unsorted debris —angular because, unlike water, glaciers do not round pieces of rock as the rocks bump into each other and into the streambed, and unsorted because ice carries sediment of all sizes and drops it wherever the ice melts. Here is a picture of a moraine deposit at the edge of Exit Glacier in Alaska. Note that there are two ridges of sediment—that is, this is a double moraine. Also, note the people in the lower left for scale. 11) Which statement best explains how a double moraine could form? The glacier initially advanced to the position of the leftmost moraine, then receded (melted) back to the right. This was followed by a second episode of advance to the left, but it halted before reaching the moraine that had already been deposited. Explanation: If the glacier passed over the rightmost moraine, it would erase the moraine because the ice would pick up the debris as it traveled over it. If the glacier passed over the rightmost moraine, it would erase the moraine because the ice would pick up the debris as it traveled over it. It is unlikely that another glacier would end at the exact same location. Water that seeps into the ground flows mostly through pore spaces in rocks below the water table. It is called groundwater, and it flows very slowly compared to surface water. Some types of rocks have more pore spaces than other types of rocks. We say that the rocks with more pore spaces have greater porosity. The ability of the groundwater to flow through the rock depends on its permeability. Groundwater has the capacity to dissolve some types of rock, especially limestone, resulting in sinkholes and caverns. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

The Water Table At some depth under virtually all land surfaces on earth, there is water in the pore spaces of the rocks. The depth at which this saturation occurs is called the water table. The water table is related to surface drainage. Currently a stream such as the one in the figure would not dry up, even if there were no rain or snow to feed it. If the stream dries up, it is because the water table is below the level of the stream channel. In that case, the arrows would point in the other direction; that is, the stream bed would feed the water table, instead of the other way around. In areas where much of the subsurface rock is limestone, groundwater may dissolve the limestone as we discussed in Lesson 29. This can form caverns, sinkholes, and even the topography seen in many Chinese landscape paintings assumed by many westerners to be stylistic. Here are photos showing examples of each of these landforms. Wells Wells are a major source of groundwater for human use. For a well to be useful and produce water, it must be drilled lower than the water table. If the water is taken from the well Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

faster than the aquifer can deliver water to the well, a cone of depression is produced. The well can run dry if too much water is taken from the well. Another way a well can run dry is if the cone of depression from another well nearby causes the smaller well to become higher than the water table. This example is discussed in your textbook and demonstrated in this animation. Unlike mineral or ore deposits, groundwater isn’t static and moves over large areas. Water-rights claims can therefore be quite complicated. Another source of concern for groundwater is any possible source of contamination. In coastal areas, seawater entering the aquifer is a large problem. Man-made pollutants can also seep into groundwater. Because the source of the groundwater can be hundreds of miles away, contamination of water can affect the groundwater, and therefore the drinking water, of people, animals, and plants far from the source. While it is possible that passage through the rocks can filter pollutants out, this does not always occur. For example, studies indicate that the source of the groundwater that feeds Ash Meadows, an oasis in the Death Valley area, is located near the Nevada Test Site, a site established for the testing of nuclear devices. It is not currently possible to say if, or how, this testing will affect the groundwater at this oasis. The time it takes the groundwater to make its journey of 50–60 km (10–37 miles) is about 15,000 years. 12) What causes cones of depression? Water is removed from one part of the water table faster than it can flow through the permeable layer that makes up the water table l So far in this unit, you have studied the earth’s interior, continental drift, plate tectonics, geologic time, and many of the effects water has on our planet. If you have time, come with us now on a virtual field trip to Rock Canyon in Utah County, Utah, USA, to see some of the geological features you have been studying about! The tour is interesting and gives good insight into how geologists think, but it’s long, about 45 minutes. If you don’t have time, everything that you need to know for the exam and unit summary exams are in the rest of the lesson and the book. Chapter 30 Quiz 1) This picture shows a valley in Oregon. Which of the following caused the features of this valley? alpine glaciers Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

2) Which of the following correctly describes how energy from the sun drives the hydrologic cycle on Earth? The energy from the sun is transferred by radiation through the atmosphere to the oceans. This radiation is strongest near the equator, and most evaporation occurs there. 3) In general, groundwater moves very slowly. TRUE 4) Which of the following statements is true concerning streams? Streams carry more sediment when moving quickly since the stream has more kinetic energy which is used to carry more sediment 5) Streams cut deep valleys as they travel through mountains, but the same streams deposit large amounts of material to form deltas when they reach the ocean. Why? When streams are traveling down steep slopes the water picks up material because it has more kinetic energy. When the water reaches the ocean, it slows down and drops that material. 6) This picture was taken near Mona, Utah. Which of the following caused the features in the image? running water (a stream) 7) This picture is of the Lena River delta in Russia. Which of the following caused the features in the image? running water (a stream) 8) The most important erosional agent of the hydrological system is which of the following? running water Chapter 30 Homework Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

1) Approximately how much of the Earth's freshwater is found in surface water (rivers and streams, lakes, marshes)? ~ 1% 2) What is the leading cause of erosion? running water (Rivers and streams) 3) What is the base level of the Mississippi River? Sea level 4) What is the wide, fairly flat land bordering the Mississippi river called? A floodplain 5) Why are flood plains desirable farm land in spite of the fact that they are prone to flooding? Because the river deposits new, mineral rich sediment every time it floods. 6) Which of the following help explain why the Colorado river cut the Grand Canyon, while the much larger Mississippi River is not in a canyon at all. a) The Mississippi moves slower. b) The Mississippi has a lower change in elevation each mile, on average. CHAPTER 31: EARTH’S CLIMATE Introduction Global warming and climate change are terms that are currently emotionally charged to many people. We often hear about the “threat of global warming” or that something must be done about climate change “before it’s too late.” But what do these terms mean anyway? In this lesson we will discuss what is meant by climate and how it is measured. We will also discuss what factors can affect the climate. Then we will take a look at what the climate has been in the past and where current data implies it is heading. Key Terms - Greenhouse effect: Visible and ultraviolet light is transmitted from the sun to the earth. This light hits the surface, is absorbed, and is changed into infrared light, which we feel as heat. The infrared light is absorbed by greenhouse gasses, trapping the heat and causing the Earth’s surface temperature to rise. - Greenhouse gas: Gasses in the atmosphere that trap heat and keep Earth warmer than it would otherwise be. Carbon dioxide, CO2, and methane, CH4, are examples of greenhouse gasses. - Milankovitch cycle: The name given to the three cycles in Earth’s orbital conditions that influence climate in regular 100,000-year, 41,000-year, and 23,000-year cycles. - Negative feedback: An effect caused by changes in climate that decreases how much the climate responds to the change. - Positive feedback: An effect caused by changes in climate that increases how much the climate responds to the change. Use the following information to answer the next 3 questions: If you have lived in a certain area for any amount of time, you may have heard someone, maybe even yourself, say something like, “Boy, it sure was hotter (or colder) when I was young.” And you’ve probably noticed that the weather can change remarkably over the period of days, weeks, and months. But what do these observations and memories mean in terms of the climate? Weather describes the fluctuations in temperature, rainfall, and so forth, over short time Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

scales, but it doesn’t necessarily describe the climate. Climate describes the average rainfall, temperature, and so forth, over a long period of time—basically the weather averaged over many, many years—and it turns out to be a lot more predictable than the weather. Just as many factors influence the daily weather, there are many factors that influence the climate. Your textbook describes many of the factors that affect the climate of a particular location. However, mountains, ocean currents, and winds aside, there are some factors that affect the climate on a global level. These factors include the sun’s effect on the earth and the gasses in Earth’s atmosphere. Milankovitch Cycles The amount of sunlight and the type of sunlight (direct or indirect) that the earth receives affects the climate of Earth. There are three ways that the sunlight can change due to the orbit of Earth around the sun. They are known as Milankovitch cycles, after the Serbian astrophysicist who discovered them. The first is how elliptical the orbit of Earth is around the sun. Over a period of one hundred thousand years, the orbit changes from quite circular to more elliptical, as Figure 31.5 in your textbook shows. Note that the amount of change in the orbit has been exaggerated to show the difference. However, when the earth is closer to the sun, the earth receives more sunlight than when the earth is farther from the sun. This difference tends to help glaciers to form. The next two changes don’t actually change the amount of sunlight received by Earth— they just change the intensity of the sunlight over certain areas on Earth. Changes in the tilt of the earth vary over a time period of about 41,000 years. In this time, Earth goes from a “larger” tilt of 24.5° to a smaller tilt of 21.5°, as shown in Figure 31.6 in your textbook and these videos from NASA. While this change doesn’t seem very large, it does seem to trigger advances of large continental glaciers. The last change is the change in the direction Earth’s axis points (i.e., the precession of the Earth’s axis) as it orbits the sun. Figure 31.7a from your textbook shows this change. This takes place over a period of 23,000 years. Over this time, the amount of direct sunlight received by the Northern Hemisphere versus the Southern Hemisphere changes. This affects the seasons too and can help cause continental glaciers to form and advance or to melt and retreat. The three configurations that help the earth heat up the most are - having a rounder orbit (as compared to more elliptical) Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

- having less tilt so that the sunlight is more evenly distributed - having a northern winter when the earth is closest to the sun. This diagram shows how these factors have changed in the past and the combined effect on the earth. The “solar forcing” component refers to the resulting changes in solar energy at high latitude due to the orbital changes. The bottom graph shows the observed glacial cycles with the gray shading showing interglacial periods. Notice that currently we are in an interglacial period (warmer period) but, according to the graph, in a short period of time (as in 1,000 years or so), we should be entering a glacial period. However, as we will discuss in the next sections, other factors affecting climate have changed. 1) According to the graph above, for the past 100,000 years, the earth spends most of its time colder than it is now Explanation: Look at the temperature under “Now” shown on the bottom graph on the left-hand side. How does this temperature compare with the overall average temperature? 2) How far apart are interglacial periods on average? 100,000 years Explanation: The peaks of the interglacial periods are shown by the gray bars on the bottom graph, Stages of Glaciation. 3) Which of the Milankovitch cycles has the biggest impact on climate? the cycle that lasts 100,000 years (changes in the shape of the orbit) Explanation: What value did you determine for how far apart the interglacial periods are, on average? Look to see if any of the cycles match the period. If you find a match, you will find the cycle that has the biggest impact on climate. Greenhouse Gasses Besides the amount of solar radiation Earth receives, the other factor that affects the global climate is how much heat is radiated back to space. This heat radiated back is largely affected by greenhouse gasses. Greenhouse gasses are gasses that allow the visible light (and higher-energy light) into the surface of the earth but block the infrared light from escaping back to space. Carbon dioxide (CO 2 ), methane (CH 4 ), water (H 2 O), and nitrous oxide (N 2 O) are all important greenhouse gasses on Earth. These gasses are very important to life on Earth. Without them, the Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

temperature on Earth would be much lower than it currently is. This video explains how the decrease in radiated energy impacts the temperature of the planet. PHY S 100 Chapter 31 | Earth's Climate In the graph below, you can see the absorption spectra of several of the individual components of Earth's atmosphere & Earth’s atmosphere total absorption spectrum at the top. The height of the line shows how much radiation is absorbed; 100% absorption is complete absorption, and 0% means nothing is absorbed. Notice how there is very little absorption in the wavelengths of the solar radiation coming in. In the wavelengths the sun emits, the total absorption is near zero. However, both the water vapor (blue line) and carbon dioxide (green line) have strong absorption bands in the wavelengths emitted by the earth. Look at oxygen (red line) and you will see even one small absorption line in this region. 4) When you compare water vapor (H 2 O) and carbon dioxide (CO 2 ) in the graph above, which is the stronger greenhouse gas? Water Explanation: Look at the value of the absorption graph for CO2 and H2O for the peak wavelength of Earth’s thermal radiation going out. Water has an absorption of over 50%, while carbon dioxide has an absorption that is under 30%. Water absorbs more energy. Proxy Data in Ice cores The textbook details several different methods we can use to determine climate conditions from times long before we were around or able to measure and record them. One of the more useful techniques comes from examining ice cores. The ice is deposited in annual bands. Each of these primarily contains water that evaporated about that year. Because the ratio of oxygen and hydrogen isotopes in the evaporated water depends directly on the temperature, these bands contain a record of global temperatures for the year. Not only is the temperature recorded, but small bubbles of air along with dust and pollen are trapped. These give a corresponding record of atmospheric composition and surface conditions. Used in conjunction with other proxy data, ice cores have allowed us to reconstruct global climate and atmospheric conditions going back nearly one million years. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Much of our information about past temperatures and greenhouse gas concentrations over the last several hundred thousand years comes from ice cores taken from continental glaciers in Greenland and Antarctica. The ice has annual layers, so we know how old each layer is, and certain measurements can be made on these layers to infer past climate conditions. This picture shows Vostok Station in Antarctica, one of the sites where ice core drilling has taken place. The textbook was written over a decade ago, so I've updated some of the information below using more recent data from the EPICA ice cores as well as the Vostok data. The photo of the ice cores shows summer layers (bright white areas) and winter layers (darker ice). Besides studying ice cores, there are other ways by which we know the climate has changed in the past. Studies of Arctic Ocean sediment tell us there have been periods of increased ice. During these periods, coarse sediment is carried by the ice and dumped in the central Arctic Ocean. We also have geologic evidence that the sea level has risen and fallen in the past—sometimes with changes of hundreds of meters. This is due to both climate change and plate tectonics. So since the climate changes naturally, what is the “big deal” right now? Climate in the Past The amount of greenhouse gasses changes with time. The amount of greenhouse gasses in the atmosphere, as measured by ice cores, correlates well with the temperature, as shown in the graphs below. They also both track together when plotted with time. To show causation, you need both the correlation between the two variables, and you need them to vary together temporally. Notice in the figures below that when the greenhouse gas concentrations are higher, the temperature is higher. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

However, while it is clear that the greenhouse gasses fit the temperature patterns well, and we know from the basic physics of radiation and greenhouse gasses that more greenhouse gas in the atmosphere produces a higher temperature, it happens that during the glacial- interglacial cycles, the greenhouse gasses were not the initial cause of warming and cooling. Instead, the greenhouse gasses were operating as a positive feedback in the system. That is, some other factor, typically changes in the amount and distribution of incoming solar radiation due to the Milankovitch cycles, would start the ball rolling toward warmer or cooler temperatures. That would then cause more or less greenhouse gasses to come out into the atmosphere, respectively, rather than being stored in the ocean or biosphere. This would enhance or suppress the greenhouse effect, and therefore cause even stronger warming and cooling trends. An example of a positive feedback mechanism is the melting of arctic ice, which both releases methane gas, a greenhouse gas, into the atmosphere and increases the amount of solar radiation absorbed by the Earth’s surface since the ice, which reflects the energy back to space, is now decreasing. This causes the temperature to increase further, melting more ice. So, why didn't the temperatures just keep increasing? Because the Earth has a balance between positive feedback like the scenario described above and negative feedback to keep temperatures relatively stable. A negative feedback mechanism is one where some factor moves the climate toward a warmer or cooler temperature but the corresponding change in greenhouse gasses in the atmosphere decreases the effect of the original change on global temperature. An example of a negative feedback mechanism would be higher global temperatures, which cause more plants to grow. The additional plants take more carbon dioxide, another greenhouse gas, out of the atmosphere. The reduction in greenhouse gas returns the temperature back to its original value. Currently, the levels of greenhouse gasses in the atmosphere are not being controlled by natural cycles involving a balance of positive and negative feedback. Humans are directly increasing the amount of greenhouse gas in the atmosphere. Because we know this will change the climate, and don't know how well the negative feedback mechanisms can be used to mitigate the changes, the scientific community is very concerned about the uncontrolled release of greenhouse gasses. (This is especially true because many of the negative feedback mechanisms rely on plants, and deforestation is another big environmental issue,) Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Current Climate Measurements First, the climate has been changing lately. Sea level has increased, arctic sea ice and alpine glaciers have been gradually melting (while some alpine glaciers are advancing, most are receding), and thermometer measurements show a net increase in global temperature. Second, human influences have been dominating natural causes of climate change for the past few decades. While natural climate drivers like solar radiation and volcanoes have been holding steady or even pushing the earth toward cooler temperatures, humans have been pumping enormous amounts of extra greenhouse gasses into the atmosphere. This increases the greenhouse effect and pushes the earth toward warmer temperatures. The extra greenhouse gasses have been winning, and the earth has been steadily warming, despite nature pushing the other direction. The big deal, then, is that if humans keep doing what we have been doing, the temperature appears likely to keep going up several degrees, no matter what natural climate drivers do. In the past, sustained temperature changes of several degrees have been associated with things like mass extinctions when most of the world’s species quickly disappeared from the fossil record. This kind of massive upheaval would certainly affect the human population as well, so even if large climate changes have happened naturally in the past, it is certainly something most people would want to avoid, if possible. Future Climate Changes So what does the future hold? Computer models of the Earth’s climate system indicate that the temperature will continue to increase somewhat even if the amount of greenhouse gas concentrations in our atmosphere remain the same. With greater increases in greenhouse gasses, we can expect even more warming. More frequent and more severe storms are predicted. Extinction of certain types of plants and animals are also predicted. Additionally, this increase in temperature will surely cause the sea level to rise. An increase of three meters would have a significant effect on our shorelines, as the figure showing the southeast portion of the United States illustrates. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Such a large increase is not out of the question over the next century, and smaller changes (which are all but certain to occur) will have large impacts in low-lying coastal areas like Bangladesh and parts of Europe. Not all the effects of climate change are necessarily bad, however. Some areas will experience an increase in agricultural productivity with a small temperature increase, for instance. But scientists and economists who study such issues have generally concluded that the negative consequences will soon far outweigh the positives if humans continue business as usual. Scientists can use the data they have about past and present climate to estimate the probability of different outcomes if humans follow one path or another, but it’s up to everyone to decide what to do about it. Should we do nothing and try to deal with climate change as it happens, hoping it’s not going to be as bad as the scientific projections indicate? Should we limit our fossil fuel use? If so, how much? Since this is a global problem, how can we ensure that everyone will limit fossil fuel use? How much money should we spend on implementing current renewable energy technology, and how much should we spend on research to develop new technologies that would be cheaper and more efficient? How much of this should come through direct government regulation, and how much should come through strategies such as tax credits for implementing renewable energy technology? There are other sources of greenhouse gasses besides fossil fuel use. Should we limit our consumption of animal products? How would that be implemented on a global scale? Finally, how do we balance the initial costs of dealing with climate change against future benefits? These are all difficult issues, but it is clear that we need to take them on, rather than abdicate our responsibility. In Doctrine & Covenants 104:13 (Links to an external site.), we read: For it is expedient that I, the Lord, should make every man accountable, as a steward over earthly blessings, which I have made and prepared for my creatures. A steward is not an owner. A steward is someone who has been given a responsibility to care for and watch over something or someone. You and I have been made stewards over the earth. As stewards, we must consider the overall impact of what we drive, eat, wear, and live on on this Earth. 5) Identify whether the following are positive or negative feedback, or not a feedback Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

mechanism at all. a) As temperatures increase, decay rates of plants increase. When plants decay they release methane, a greenhouse gas. Positive - more greenhouse gasses means more increase in temperature b) As temperatures increase, people use more energy for air conditioning, and that energy comes from fossil fuels. Positive - more greenhouse gasses means more increase in temperature c) As temperatures increase, plants grow more rapidly, removing carbon dioxide. Negative - less greenhouse gasses means a drop in temperature d) As temperatures increase, there are more violent storms increasing the amount of erosion. None - this erosion doesn’t directly affect temperature. e) As temperatures increase, more water evaporates increasing the humidity of the air. Positive - more greenhouse gasses means more increase in temperature and water vapor is a greenhouse gas….though if the vapor condenses and makes clouds that block the light that would be a negative feedback process. Chapter 31 Quiz 1) Identify each of the following as a positive or a negative feedback mechanism. a) As water temperatures increase, the solubility of gasses in the water decreases, so the oceans release carbon dioxide - Positive b) As surface temperatures increase, the rate of plant growth increases, removing carbon dioxide from the atmosphere - Negative c) As surface temperatures increase, the amount of the surface covered with snow and ice decreases - Positive d) As surface temperatures increase, decay rates for vegetation increase. Decaying plants produce methane - Positive 2) Refer to this chart showing variations in temperature over the last four hundred thousand years. Note that the present day is shown to the left of the graph. Based on the natural cycles found in the graph, what would you predict the climate will be like in fifty thousand years? The climate will be cooler than it is now. 3) Which of the following best describes the behavior of greenhouse gasses? Greenhouse gases do not interact with visible light, but absorb longer-wavelength, infrared light, inhibiting the longer wavelengths from being radiated into space. 4) Global temperatures have increased over the last 100 years. What evidence is there that Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

human activities are at least partially responsible for this increase? Ice cores show a correlation between global temperature and CO2, and humans have released a lot of CO2 in the last 100 years. 5) Which of the following is solely a natural factor that influences climate? (A natural factor is one that is not related to human activity.) the amount of energy the sun puts out 6) Which of the following provides proxy data that can be used to estimate temperatures in ancient climates? Select one. The thickness of tree rings in ancient wood Chapter 31 Homework 1) The data from the EPICA and Vostok ice cores is plotted below. Look at the graph and identify the period of the dominant pattern on the graph. Which of the Milankovich cycles match that period? 100,000 change in how circular the Earth's orbit is (eccentricity) The other Milankovich cycles can also be seen on the graph. Look at the graph and identify those patterns too. The three main surfaces on the Earth are water, land, and snow. Explain what happens to energy from the Sun that is incident on each of these surfaces. What feedback mechanisms come into play with each surface? What role does each type of surface play in determining global temperature? 2) What happens to energy from the Sun that is incident to water? It is reflected when the sun is at sharp angles and absorbed when the sun is overhead. 3) When energy from the sun is absorbed by the oceans, they warm. Which of the following are positive feedback loops involving a warming ocean? a) As the ocean warms, the solubility of dissolved gasses drops, and the ocean will release carbon dioxide back into the atmosphere. b) As the ocean warms, more water evaporates. Water vapor is a greenhouse gas. 4) What happens to energy from the Sun that is incident on land (dirt or plants, not snow)? It depends on what is on the land. Some surfaces reflect and others absorb. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

5) When energy is absorbed by the land, it warms. Which of the following are positive feedback loops involving the land. a) As the land warms, permafrost melts releasing methane into the air. b) As land warms, plants die and stop absorbing carbon. 6) What happens to energy from the Sun that is incident to ice and snow? It is primarily reflected 7) When a surface is covered with snow, it is more reflective. Is this going to create a positive or negative feedback loop? Positive CHAPTER 32: BEYOND EARTH Introduction In this lesson we will begin to examine what is beyond Earth, specifically our own solar system. When you look at the sky at night, most of the stars you see are actually stars. But there are a few “stars” that are not stars at all—they are planets. With a telescope, you can even see the rings on Saturn and the Galilean moons orbiting Jupiter. Key Terms - Distance ladder: A method used in astronomy where greater and greater distances are determined using many different measuring techniques that overlap to establish a sequence of increasing distances. - Jovian planets: The outer gaseous giant planets: Jupiter, Saturn, Neptune, and Uranus. - Laser ranging: A technique for measuring distance that is similar to radar ranging, but instead of reflecting microwaves, laser light is reflected off a nearby surface, and the time for the reflected pulse is observed. - Light year: The distance light travels in a year, approximately ten trillion kilometers. - Lunar highland: The old, heavily cratered terrain on the moon that is thought to contain material from the original lunar surface. - Maria: The large, generally crater-free lava plains commonly found on the side of our moon that faces Earth (singular: mare). - Nebular hypothesis: The idea that the sun, the planets, and other objects in the solar system all formed from a single gigantic cloud of gas and dust. This hypothesis explains the major features and structure of our solar system. - Radar ranging: A technique for measuring distance in which pulses of microwaves (radar) traveling at the speed of light are sent to a nearby object, and the reflected pulse is timed to determine the distance. - Terrestrial planets: The inner rocky planets: Mercury, Venus, Earth, and Mars. - Triangulation: A distance-measuring technique that involves observing the angle to a distant object from at least two different locations with a known separation. It is then possible to determine the unknown distance by comparing the observed angles. Use the following information to answer the next 2 questions: The closest planet to Earth is Venus, but how far away is it? While the answer varies because of the elliptical orbits of the planets, the average distance between Earth’s orbit and Venus’s orbit is 42 million km (26 million miles). The sun is 150 million km (93 million miles) from Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Earth, on average. For the non-astronomer, these distances seem a bit hard to comprehend! But to an astronomer, these distances are small. So how are these “small” distances—distances within our own solar system—measured? As we move beyond our solar system, the distances become even harder to understand. How do astronomers measure these distances? What does it mean? The video below provides a great summary. To view it, however, you will have to click the link to watch it on YouTube. How big is the universe ... compared with a grain of sand? Radar and Laser Ranging Radar ranging and laser ranging are the methods of choice for the small distances inside our solar system. With radar ranging, a radar beam is pointed at the object of interest (usually a space probe orbiting a planet or moon). The radar bounces off the object, and the travel time is measured. Because the radar beam is electromagnetic radiation, we know the speed is the speed of light. With the time of flight and speed of light known, we are able to determine the distance to the object—as this animation demonstrates. It takes 2.6 seconds for the light to get there and back. Distance = time × velocity, so put 1.3 seconds in for the time (half of the round trip time), 300,000 km/s as the speed, and the resulting distance is 390,000 km. Laser ranging is a variation on the same technique in which a laser is used instead of a radar beam. Besides using a laser instead of microwaves, the idea is the same. The beam from a laser travels at the speed of light because it is light. Triangulation Radar ranging is used for “small” distances, but the distance to even the closest of all other stars is amazing. If you made a model of part of the universe, with the earth one meter from the sun, the nearest star to the sun in your model would be 271,000 km away—that’s roughly 70% of the way to the moon from Earth in real life. By the way, in a model built to that scale, the sun would be only 9 millimeters across, and the earth would be a speck about nine hundredths of a millimeter in diameter. Expressing distances to stars in kilometers soon becomes unwieldy, so we use light-years instead. A light-year is the distance light travels in one year—about 9.4 × 1012 km, just less than 6 trillion miles. The distance to Proxima Centauri, the nearest star to our sun, is 4.3 light-years. This distance can be determined by geometrical triangulation. Geometric triangulation uses triangles and geometry. The angle the star makes relative to very distant background stars is measured as Earth orbits around the sun. We know the distance from the sun to Earth, so we have an angle and a side. From this information and some geometry (or trigonometry), we can determine the distance of the other side of the triangle—the distance from Earth to the star. Stars that are farther away have a smaller angle and stars that are closer have a larger angle, much like how objects that are far have less of a shift when you look through your right eye compared to your left eye and compare that shift with the shift of an object that is close to you. This animation demonstrates this idea. The distance that can be determined by triangulation depends only on accurate measurements, not on any astronomical theory, so the more accurately the very small angle can Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

be measured, the more accurately distances can be determined. The Hipparcos satellite, which completed its mission in 1996, increased the number of stars whose distance can be determined by triangulation to 120,000 and pushed the distance out to 3,000 light-years. Radar ranging and triangulation are the first in a series of steps. Geometrical triangulation using stellar parallax is the first rung on the distance ladder used by astronomers. Radar ranging was used to verify distance measurements in our solar system made by triangulation. Triangulation was, in turn, used to verify distance measurements made by brightness-distance methods. Brightness-distance methods were then used to verify distance measurements made by cosmological redshift. In a sense, astronomers “stood” on the previous measuring technique to reach the next step in measuring distance, much like you and I stand on a lower rung of a ladder to climb higher up the ladder. Brightness-Distance Imagine someone walking toward you holding a flashlight at night. The farther away they are, the dimmer the flashlight looks. As they get closer, the amount of light that hits you increases. There is a mathematical relationship between the distance of the flashlight and the brightness you see, which is described in the video below. Demo of how distance from an EMF source reduces signal strength As long as you know how bright a light source is, you can calculate how far away it is. In case you are wondering how to do this, the equation to determine distance (d) is , where M is how bright the star really is and m is how bright the star appears to be. The trick in using this equation is how to determine how bright the star really is (M). In Lesson 33, we talk more about how stars produce light. Understanding this process allows us to determine how bright a star actually is based on the colors of light it produces. From there, astronomers are able to calculate how far away stars are. By the way, the distance equation shown above won’t show up on any quiz or exam. I included it in case you were curious. Doppler Shift As we look at the distance ladder, we find that radar ranging doesn’t get us out of the solar system. Geometrical triangulation using stellar parallax is considered the first rung on the distance ladder used by astronomers. Brightness-distance methods are the next steps. Doppler shift is the last rung of our ladder, and it takes us to the farthest distances. We will discuss the last two methods in more detail in Lessons 33 and 34. The use of the Doppler shift to determine distances of galaxies is explained in this video: Redshift Just to clarify part of the video and explain that, contrary to how the galaxies are shown in this video, the actual galaxies themselves do not appear bluer in color if their spectral lines are shifted toward the blue frequencies (blue shift), nor do the galaxies appear redder in color if their spectral lines are shifted toward the red frequencies (red shift). The terms blueshift and redshift apply to the absorption lines, not to the overall color of the galaxy. 1) The distances to the nearest 100,000 or so stars can be measured by which of the following techniques? Triangulation Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Explanation: redshift - this technique is used to measure the farthest distances visible in our universe; brightness-distance techniques - this technique is used to measure distances beyond the near 100,000 stars; radar ranging - this technique is used to measure distances in our solar system only. 2) Which of the following methods are used to measure distances between objects in our own solar system? a) radar ranging b) Triangulation Explanation: redshift - this technique is used to measure the farthest distances visible in our universe; brightness-distance techniques - this technique is used to measure distances beyond the near 100,000 stars Opportunities to directly measure the properties of the planets are rare. Most of what we know about the solar system we’ve figured out through indirect processes—we’ve only gone to one other location, the moon, and brought back samples. We don’t require physical samples, though. In Units 1 and 2, we learned some scientific principles that we can use here. Mass We can determine the mass of any planet by measuring the gravitational acceleration. As we learned in Lesson 3, heavy objects and light objects dropped near the surface of the earth all fall at the same rate. That gravitational acceleration is determined by the radius and mass of the earth and does not depend on the mass of the object being dropped. The same is true for any planet. If you measure the gravitational acceleration, you can calculate the mass of the planet. Gravity is what keeps things in orbit. An orbiting object is actually falling toward the thing it orbits. Because this concept is always one of the most commonly misunderstood, and Unit 1 was a long time ago, the video below provides a quick refresher. Is There Gravity In Space? So, to sum it all up, we know the masses of the planets and other objects in our solar system because: a) All we need to do in order to figure out the mass of a planet is to measure the planet’s gravitational acceleration. b) An orbiting object is falling. By measuring the orbit of any orbiting object, we know the gravitational acceleration. We don’t need to know the mass of the orbiting object! Composition Another physical property we can determine from Earth is composition. The video describing how the Doppler shift is used to measure whether a galaxy is moving toward us or away from us mentioned the absorption spectra of gasses. We talked about this absorption spectra in Unit 2. We use absorption spectra as well as emission spectra (also discussed in Unit 2) to determine what gasses are present in a planet’s atmosphere or what gasses make up a star. The video talks about how we know the composition of planetary and stellar atmospheres: How Do We Know What Air is Like on Other Planets? History The closest non-manmade object to Earth in the solar system is our moon. If you look at Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

the moon even without a telescope or binoculars, two distinct types of terrain can be seen. One is the bright, heavily cratered lunar highland. The lunar highland continues on behind, on the “dark” side of the moon that never faces Earth. The second type of terrain is the darker, smoother terrain known as the maria (singular: mare). Using the principle of superposition that we discussed in Lesson 28, we determine that the lunar highlands, caused by intense meteor bombardment, formed first across the entire moon’s surface. The maria, which are chemically different from the highland, were formed afterward by large asteroids crashing into the moon’s surface and melting the surface. Lava flows filled in the large impact basins. Periodic impacts occurred later, as indicated by the bright craters seen on top of the maria. The video demonstrates how this could happen: NASA | Evolution of the Moon We can use the same ideas to puzzle out histories for the inner, rocky planets of our solar system as well as the moons and dwarf planets throughout our solar system. Curious about how the moon itself was formed? The video shows the currently accepted theory: Where Did The Moon Come From? - Do We Really Need the Moon? - BBC The eight major planets, as well as their moons, are remarkably diverse in terms of their sizes, chemical makeup, and visible surface and geologic features. These eight planets are broken into two separate categories: the terrestrial planets (the planets similar to Earth) and the Jovian planets (the planets similar to Jupiter). Terrestrial Planets The terrestrial planets consist of the four inner planets: Mercury, Venus, Earth, and Mars. They are characteristically small, dense, rocky planets. They have hard surfaces and small atmospheres, at least compared to the Jovian planets. Jovian Planets The Jovian planets consist of the four outer planets: Jupiter, Saturn, Neptune, and Uranus. They are characteristically large, low-density, gaseous planets. They have large masses to go with their large sizes, and very large atmospheres that appear to surround a rocky core. They all have ring systems, although Saturn’s is the best known. If you would like to know more about the planets, Activity 32.1 includes more information. However, you will not be tested on it—it’s just for your own edification! 3) Which of the following are known or expected to be different for Jovian and Terrestrial planets? Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

a) Size b) Mass c) Density Use the following information to answer the next 3 questions: A good model for the formation of the solar system will account for all of the features we observe about the solar system. It has to explain why the planets orbit in a flat plane, why there are two groups of planets with different densities (terrestrial and Jovian planets), and finally, why the moon, Mercury, etc. are covered with craters. Our current model, which is still a work in progress, is called the nebular hypothesis. According to the nebular hypothesis, the solar system is thought to have formed from a condensing cloud of gas and dust. Most of the mass formed the sun. We will discuss stellar formation more in Lesson 33; however, in this lesson, we will discuss the formation of the planets. As gravity pulls the cloud together, it flattens out into a disk due to conservation of angular momentum. This is described in the video: Why is the Solar System Flat? The planets were formed when regions of higher density in the flattening outer disk drew in material by the force of gravity. Comets and asteroids are also remnants of the solar nebula. Eventually the cloud of gas and dust became a central star (or stars, in the case of various other solar systems) orbited by planets and smaller bodies. According to the nebular hypothesis, as the cloud collapsed, gravitational potential energy was converted into kinetic energy. Eventually the center became very hot and dense. This temperature difference is responsible for the differences in the terrestrial and Jovian planets that you see in our solar system today. Due to the increased temperature near the center of the cloud, only material with a high melting temperature could condense to form planets. If you remember back to our previous discussions in Lesson 12 and Unit 3 (see Lessons 19, 21, 22, and 23), metals and metal compounds have higher melting temperatures, so the terrestrial planets could have rocky and more metal-rich compositions. Covalently bonded molecules have lower melting temperatures, so the Jovian planets that formed farther from the center where it was cooler were able to form with hydrogen, helium, methane, ammonia, and so forth. The nebular hypothesis also can explain why the ages of the planets and the sun seem to be the same. The ages are the same because they formed from the same cloud of dust and gas. Also, all the planets orbit the sun in the same direction because they formed from the same cloud of gas and dust that was spinning in one direction. For another look at the nebular hypothesis, watch this video: PHY S 100 Chapter 32 | Beyond Earth 4) The principal reason why the inner planets and the outer planets have very different compositions is their original positions in the young solar nebula . Explanation: INCORRECT ANSWER: they came from different places in the galaxy - the material that formed the solar system mixed together as it orbited. Even if it had come from different parts of the galaxy, which it didn’t, the spinning, contractions, and collisions would have mixed the elements and molecules in the gas cloud. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Explanation: INCORRECT ANSWER - the laws of chemistry change in the outer solar system According to the self-evident truth position symmetry, we know that the laws of nature are the same no matter where we are in the universe. 5) Where is the proto-planetary disk (the cloud of gas that is turning into a solar system) the hottest? In the middle Explanation: The outer edges are farther from the protostar (the middle portion of the gas that is heating up and starting to turn into a sun). The protostar is the source of heat, so the region closest to the protostar will be the hottest. 6) In order to form a planet, individual atoms and molecules must first stick together. What types of materials will be solid in the inner parts of the disk? Pick all that apply. a) Metallic b) Ionic Explanation: Covalently bonded materials have lower melting and boiling temperatures, so at higher temperatures, these molecules would be liquids and gasses. You might now be wondering, “If the nebular hypothesis is the preferred hypothesis for solar system formation, is there any evidence that this process is happening elsewhere?” The answer is yes, twice. a) In recent years, evidence that some nearby stars are accompanied by planets has been accumulating quite rapidly. The sensitivity of the techniques available to astronomers permits only very massive planets to be detected more easily, but planets just a few times more massive than Earth have also been detected. b) The Hubble Space Telescope (HST) has revealed the presence of flattened disks of gas and dust around several stars. These disks are particularly prevalent around young, newly formed stars. This is consistent with the idea that the matter has not yet had time to condense into planetary systems. Look at the image of the Orion Nebula from the HST below. The Orion Nebula can be seen with the unaided eye (and can be seen even better with simple binoculars or the HST). It is south of the belt of Orion in the Orion constellation. Notice the inserts in the picture. These inserts show objects known as “proplyds,” or protoplanetary disks (these are not terms you need to remember). The Orion Nebula seems to have the lion’s share of proplyds, but we can find evidence supporting the nebular hypothesis elsewhere. In the pictures below, we see extremely young stars located in the constellation Taurus. Each picture below is a hot young star surrounded by a disk of gas and dust that happens to be edge-on to us. They are photographed in infrared light, which penetrates the dust better than other wavelengths. In case you are wondering how large these disks of gas and dust are: The scale bars on each photograph are 500 astronomical units (AU) long, and an AU is the mean distance from the earth to the sun (155 million km). The dwarf Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

planet Pluto is about 40 AU from the sun, on average, so these disks are still very large. We’ve been able to detect planets around so many stars that we currently believe that most stars have planets. One surprising finding was that some of these planets are Jupiter-like planets orbiting closer to their stars than the orbit of Mercury. The nebular hypothesis says that a Jovian planet cannot possibly form that close to a star. As scientists, breaking a model is very exciting. In unit 2, you learned about some of the big steps in understanding (and the accompanying Nobel Prizes) that resulted from experiments whose results contradicted the predictions of the current models. However, it turns out there is no contradiction or need for a new model here. Astronomers realized that those planets had actually formed far from their star beyond the frost line and moved inward. Because of conservation of angular momentum, once a planet gets big enough to gravitationally sweep up gasses out of the disk, its orbital speed will decrease as its mass increases. This will make Jovian planets migrate inward towards the star as they grow. Once the gas disk is dispersed by energy from the star, the inward movement stops. This process can easily explain hot Jupiters without the need for a new model. Chapter 32 Quiz 1) What would be the best method to determine the distance to Mars? Bounce a radio wave off of it and time how long it takes to make the round trip. 2) Which of the following are true of the Jovian planets? The Jovian planets are larger in both mass and volume than the terrestrial planets. 3) Which of the following lists represents the terrestrial planets? Mercury, Venus, Earth, Mars 4) The outer planets are much more massive and much lower density than the inner planets. What conditions in the disk of gas and dust that surrounded the protostar led to the difference between the Jovian and terrestrial planets? A protostar is that glowing central accumulation of matter in the disk of gas and dust that became the sun. The Jovian planets formed in the colder outer regions of the disk where the temperatures were low enough for low density materials like water and methane to form solid ices. 5) What would be the best method to determine the distance to Proxima Centauri, the star nearest to our sun, at a distance of 4.3 light years away? Take pictures of Proxima Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Centauri 6 months apart and measure how far it has traveled though the sky in that time relative to the background stars. 6) The outer planets are much more massive and much lower density than the inner planets. Why did they form that way? Planets form from solids. Near the sun, only rock and metal were solid. Further away, low density material solidified. 7) How can you determine the mass of a planet you haven't been to? Measure the motion of something that orbits the planet. 8) How can you determine the chemical composition of the atmosphere of a planet you haven't been to? Measure the spectra of light it emits. Chapter 32 Homework The current model for how planets form is known as the nebular hypothesis. As discussed earlier, a good scientific model needs to provide explanations for all of the observations made to date, and predict things that can be measured with future experiments. You need to be able to describe the nebular hypothesis of the Solar System in terms of how we judge scientific models. a) How does this model explain the major features and characteristics of the Solar System? Why are there Terrestrial and Jovian planets? Why do all of the planets orbit in the same direction? b) We've recently become able to detect planets around other stars. What does the nebular hypothesis predict we'll find as we become able to better measure the orbits, mass, and composition of these planets? c) Jupiter like planets that orbit even closer to their star than Mercury in our solar system, known as "hot Jupiters" have been discovered. Why was the existence of "hot Jupiters," initially thought to be a problem for the nebular hypothesis? How does the nebular hypothesis explain this? 1) The protoplanetary disks vary in temperature. The material closest to the center is the hottest and the material farther out is colder. The "frost line" is an important dividing line between the inner and outer solar system. Why? Because planets are built out of material that is solid, and past the frost line, planets are made of ices as well as rock.. 2) According to our theory of solar system formation, why do all the planets orbit the Sun in the same direction and in nearly the same plane? a) Because there was a small amount of angular momentum in the nebular the solar system formed from, and that angular momentum was conserved as the disk collapsed. 3) Why are the inner planets made of denser materials than the outer planets? a) In the inner part of the nebula only metals and rocks were solid because of the high temperatures, whereas hydrogen compounds, although more abundant, were only solid in the cooler outer regions. 4) We've recently become able to detect planets around other stars. What does the nebular hypothesis predict we'll find as we become able to better measure the orbits, mass, and composition of these planets? Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

a) That most solar systems should have all of the planets orbiting in a disk in the same direction. b) That most solar systems should have rocky planets close to the star and gas planets farther away. 5) Jupiter-like planets that orbit even closer to their star than Mercury in our solar system, known as "hot Jupiters" have been discovered. The existence of "hot Jupiters" was initially thought to be a problem for the nebular hypothesis. How does the nebular hypothesis explain this? a) The frost line for some stars is much closer than it was for our sun. b) The hot Jupiter planets formed farther away from their stars and then moved closer. CHAPTER 33: THE LIFE CYCLE OF A STAR Introduction Think back to the last clear night when you had the opportunity to go outside for a little while and look at the stars. Did you notice that stars come in different colors? There are red stars and bluish stars in addition to the standard yellowish stars. Were you able to see the Milky Way? How about Polaris, the North Star? Or maybe you could see the Southern Cross instead? Over our lifespan (and those of our parents and grandparents), most stars seem to be unchanging in both position and brightness. It is rare to observe major changes in any one star, but as we look at enough stars, we see “snapshots” of the different evolutionary stages that have been predicted by astronomers. In this lesson we will examine the evolutionary changes for different sizes of stars. As we look at the history of the star, some old friends will show up— gravity, the electromagnetic force (pressure), nuclear fusion, and conservation of mass-energy, to name a few. Key Terms - Absolute brightness: See absolute luminosity. - Absolute luminosity: The actual amount of energy radiated from an object. - Apparent brightness: How bright a star appears to an observer on Earth. It is a measure of the absolute luminosity of the star as affected by the distance from the star to Earth. - Black dwarf: The remains of a sun-sized star that has gone through the white dwarf phase and cooled down so that it no longer emits light. - Black hole: An object where gravity is so strong that not even light can escape from its surface. - Brown dwarf: An object that is like a star except it is too small to sustain fusion in its core. - Cepheid variable star: A star whose brightness oscillates with time—the absolute luminosity of the star is related to the length of time it takes the star to vary in brightness. - H-R diagram: See Hertzsprung-Russell diagram. - Hertzsprung-Russell diagram: A plot of absolute luminosities for nearby stars versus the colors of those stars. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

- Hydrogen burning: Hydrogen fusing to helium. - Interstellar medium: The atoms, ions, and molecules that exist in the vast spaces between stars. - Main sequence: (1) Position on the H-R diagram where the majority of the stars fall; (2) stage of a star in which hydrogen fusion is occurring in the core of the star. - Neutron star: The remaining material at the center of a supernova explosion that is composed almost totally of neutrons. The entire mass of our sun would be in a sphere a few tens of kilometers in diameter. - Planetary nebula: A glowing shell of gas that has been blown off an old star. Planetary nebulae form during the red giant phase of a star. - Protostar: An early stage of the formation of a star in which fusion has not started but the cloud glows due to the acceleration of charged particles. - Pulsar: A radio source that is thought to be a rapidly spinning neutron star. - Red giant: A large, bright, “cool” star that has exhausted most of the hydrogen fuel in its core. - Supernova: The explosion of most of the material in a star, resulting in an extremely bright, short-lived object that emits a vast amount of energy. This explosion creates the heavier elements found in the universe. - Supernova remnant: A glowing shell of gas that was ejected from a supernova as well as the interstellar material that is swept up by this expanding shell of gas. - Type 1A supernova: A type of supernova whose maximum brightness is always the same. It is, therefore, useful in determining distances. - White dwarf: A small star that no longer sustains nuclear fusion and has shrunk to become a dense object about the size of Earth. In order to see an object, photons from that object have to get to a detector. The bigger the detector, the more photons it collects, which allows you to see fainter objects. Below is a video showing a series of images of the same cluster of stars. The only thing that was changed was the aperture of the telescope (i.e., the size of the opening in the telescope increased). Notice how more faint detail appears as the aperture gets larger. Is telescope aperture important? Astronomers use the information gained from these photons and telescopes to learn more about stars. Due to the incredible number of stars and gas clouds visible with telescopes, astronomers are able to determine quite a bit about the phases in the life cycle of various types of stars. The figure below gives an overview of the stellar evolution and how it varies with mass. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

To really give you a good framework upon which to hang all the material we will discuss in this lesson, watch this overview video: PHY S 100 Chapter 33 | History of a Star 1) Why does a telescope let you see astronomical objects better than your naked eye? a) Telescopes can be hooked to a detector that is more sensitive to a wider range of photon energies than your retina. b) Telescopes are bigger in diameter than your pupil so they collect more photons. Explanation: You could debate this depending on how you define magnification. The real moon is much bigger than the image created by a telescope. And galaxies are enormous, while the image fits easily into the 1.25" eyepiece. They're actually taking a huge object really far away and making a little image, and inch or so across, that is much, much closer. So, it is not making the object bigger. However, that 1" galaxy that is projected so it appears to be a couple of inches in front of your face will take up a larger portion of your field of view than the actual galaxy that is 100,000 light years across but 100's of millions of light years away. Molecular Clouds The empty space between stars isn’t really empty. It contains small amounts of matter, mostly hydrogen with some helium and trace amounts of other atoms and molecules. Random fluctuations in density allow gravity to pull this interstellar medium together into huge clouds of gas. Within these clouds, gravity can pull the material in the densest regions together to form the beginnings of a star. This image shows a molecular cloud—the name for these huge clouds of gas. In this particular molecular cloud, a star has formed at the top of the image and is pushing the remaining molecular cloud away from it due to the star’s radiation of mainly light but some particles. This pushing (the result of the electromagnetic force) is causing the remaining molecular cloud to contract even faster and causing new stars to form in the molecular cloud. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Protostars Imagine a huge (and that means huge) cloud of gas and dust—mostly hydrogen but with small amounts of other elements mixed in—that is loosely held together by its own gravitational attraction. Here is an example of such a cloud. While this picture looks like something you might see when watching a science-fiction movie, what you are seeing is a picture taken by the Hubble Space Telescope. It is only part of a giant molecular cloud about 5,000 light-years away from us. Each of the columns of gas you see is several light-years tall. (The dark black area in the upper-right corner is where no data was obtained.) How does such a structure form? Most of interstellar space is a better vacuum than we can produce in laboratories on Earth. Pause! Let’s pause for a moment to clarify the term vacuum. In this sense, a vacuum is a volume of space where the amount of atoms and/or molecules is much, much less than what we find on Earth. It is not a cleaning tool used to clean floors or vacuum up dust. Unpause—back to the interstellar medium! The few atoms in a cubic meter of the interstellar medium are heated to very high temperatures by ultraviolet radiation from surrounding stars. Here and there, however, are fairly dense clouds left over from galaxy formation. These clouds are dense enough to shield their interiors from this radiation. Therefore, they are fairly cool and molecules can form. Like terrestrial clouds, they are clumpy and irregular, and they tend to collapse in places because of local concentrations of gas. Now look at the following video, which zooms up to a closer view of the pillars. As you look at the video, notice the “fingers” of gas and dust that are being isolated by the ultraviolet radiation that evaporates the surrounding gas. Can you spot some of the globules Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

that have been completely isolated from the cloud? These are clumps that are bound together by their own gravity. They will continue to collapse to become stars. However, at present they are still larger than our entire solar system! We call these spots protostars, meaning “early stars.” As they collapse, gravitational potential energy decreases and kinetic energy increases. As the temperature continues to rise, collisions between the atoms increase. The cloud begins to glow from thermal emission (much like the burner on an electric stove glows when it gets hot). These clouds or protostars are not yet stars, though, in the technical sense of the word, because they are not powered by nuclear fusion. 2) We start calling a dense clump in a molecular cloud a protostar once the atoms in the "dense clump" have enough energy to produce infrared photons. Where do protostars get the energy to be hot enough to glow in the infrared? Gravitational potential energy. The atoms in the cloud have fallen a long way so they're moving fast. Use the following information to answer the next 3 questions: As a protostar collapses under its own gravity, it becomes smaller in size, and collisions among its atoms increase in frequency. The temperature keeps going up, converting the gas into plasma. Eventually, if the protostar has enough mass, it reaches about ten million degrees Celsius in the core of the star. At that temperature, the hydrogen nuclei have very high speeds, and even though there is an electromagnetic repulsion between them (because they are of like charge), they get close enough to each other for the strong force to take over before the repulsion stops them. This results in nuclear fusion, which releases immense amounts of energy as part of the mass of the nuclei is turned into energy. On the other hand, if the mass of the cloud is not enough to cause high enough temperatures, fusion will not begin and the cloud ends up as a brown dwarf. Assuming the protostar has enough mass and fusion begins and continues, the outward pressure generated inside the star due to the electromagnetic force caused by collisions of gas particles in the star matches the force of gravity pulling inward. A balance is struck, and the star stops collapsing. This marks the beginning of its mature life. Most of the life of a star—about 90% of it—is spent in this stage called the main sequence phase. Deep in the star, hydrogen is fused to form helium. Astronomers often call this the hydrogen “burning” phase of a star’s life. Hydrogen is not really being burned as it was in the demonstrations you saw previously in Lesson 20. Fusing the hydrogen together produces a lot more energy! The heat produced radiates from the core outward, eventually reaching a zone of convection that transfers the heat to the surface of the star. This is what we see—not the nuclear fusion, but the light that results from transmitting that energy to the surface. The temperature at the surface is far below the temperature required for fusion. Now let’s think about how mass could affect this stage of a star’s life by asking (and answering) a few questions. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

3) Let’s say you have two stars. These stars have different masses. If you compare the gravitational force holding the star with small mass together with the gravitational force holding the star with large mass together, which of the following is true? The star with larger mass experiences a larger gravitational force. Explanation: The gravitational force depends, in part, upon mass. Remember from Lesson 3 that an object with larger mass experiences a larger gravitational force. 4) If you compare the outward force due to the electromagnetic force caused by collisions of gas particles inside the star which is required to balance the inward gravitational force on two different stars with two different masses, what will you find? The star with larger mass will require more outward pressure to balance gravity. 5) If you compare the amount of fusion necessary to balance the inward gravitational force on two different stars with two different masses, what will you find? The star with larger mass will require more fusion to balance gravity Explanation: The star with larger mass has a higher inward gravitational force. A larger outward pressure is required to balance this larger gravitational force. This larger outward pressure is achieved by more fusion, which releases more energy, which causes the temperature to rise. This rise in temperature increases the pressure. How long the star remains in this main sequence stage depends on its mass. If it is a very massive star, then it will use its supply of fuel very rapidly and last a relatively short time. The smallest stars last the longest. A star like our sun is considered a small star. It will last for about 10 billion years before it leaves maturity for the next stage of its existence. This means that, according to our best estimates, we have 5 billion years left. Small stars are far more common than larger stars. This is true because far more small stars than "medium" or "large" stars form out of molecular clouds and also because once they form they outlive their larger siblings. While scientists are still trying to figure out why small stars are more common to start with, why they live longer is much easier to understand. If a star has more mass, there is a larger gravitational force trying to collapse the star. So, it will need higher temperatures to produce a larger electrical force to balance gravity. This means large stars have a higher rate of fusion and burn through their fuel much faster. Use the following information to answer the next question: Sooner or later, the balance between gravitational collapse and internal pressure is disturbed as the supply of hydrogen in the core of the star diminishes and nuclear fusion in the core decreases and even subsides. Because fusion is not occurring in the core of the star, gravity is able to overcome the internal pressure that has decreased, and the star begins to collapse. This collapse heats up the volume just outside the core to temperatures at which hydrogen that was previously unable to undergo fusion now can fuse. H-He fusion in this layer outside of the core begins. This creates large internal pressures that overcome gravity and push the outer layers of the star away from the core, causing the outer layers of the star to expand to dozens of times their original diameter. The star becomes very large, and its surface cools until it is only red hot. When our sun becomes a red giant star, Venus will be engulfed within it. The image below shows a kind of transparent view of a star as it moves into its red giant phase. The bright yellow sphere in the center is the core, and it consists mostly of helium. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Notice that it looks very hot, and it is—but not hot enough to support the fusion of helium to carbon. It is hot enough for hydrogen fusion, but the core is out of hydrogen, and the core is not hot enough to support the fusion of helium to carbon. 6) Why are higher temperatures necessary to cause helium to fuse to carbon? Helium nuclei have a higher charge than hydrogen nuclei do, so more kinetic energy is necessary to overcome the electromagnetic repulsion and allow the nuclei to get close enough for the strong force to take over. Explanation: If you look at the periodic table and compare hydrogen (H) and helium (He), notice that hydrogen has one proton while helium has two protons. What does this tell you about the electromagnetic repulsion between two helium nuclei when compared with the electromagnetic repulsion between two hydrogen nuclei? Eventually the helium core is compressed enough that it reaches around 200 million degrees. Helium fuses to carbon explosively, dispersing the nuclei so that fusion again shuts down. Gravity once again begins to collapse the star, and within a few thousand years, this red giant phase has ended. It may not be the last one, though. If the mass of the star is large enough, the helium in the shell around the core will begin to fuse helium into carbon, and the same sequence of events will be repeated, leading to another expansion in a second red giant stage. Our sun will have a second expansion, and this time it will be large enough to swallow Earth. It will go faster, though, and if it is followed by a carbon-to-oxygen-and-neon-fusion stage, that will be faster yet. Even faster episodes of collapse, expansion, and renewed fusion leading to the production of heavier nuclei in the interiors of the stars can follow. The largest stars can produce elements as heavy as iron in their cores. During the final stages of a star’s life, the hot gasses that make up the outer layers of the star are pushed into space. These gasses are called a planetary nebula. They form glowing clouds surrounding the dying star like the planetary nebula shown below. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Use the following information to answer the next 6 questions: How a star dies depends on its mass. The smallest stars end up as white dwarfs and eventually black dwarfs. The more massive stars end up going supernova, and a neutron star then remains. The most massive stars of all experience a supernova and then turn into a black hole. Because all stars lose mass during the red giant stage, the bounds of “small,” “medium,” and “large” are approximate. White Dwarf and Black Dwarf A star with mass up to eight times the mass of our sun, more or less, will end its life as a white dwarf, producing a spectacular planetary nebula along the way. As the star’s nuclear furnaces shut down, gravitational collapse begins (this scenario should sound pretty familiar by now). Layers outside the core, which consist of helium and hydrogen, reach temperatures at which they undergo explosive fusion. When helium fusion occurs in small stars, there isn’t enough gravitational force to hold on to the outer layers of the star. This time, it is not a red giant that is formed. These outer layers expand away from the star, and a planetary nebula is formed. Several planetary nebulae are shown below. You can click on the arrow to see the next planetary nebula in the slideshow. Planetary nebulae take shapes that range from the expected spherical to the very strange, apparently governed by magnetic fields in the star and whether there are other stars in the system. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

When the planetary nebula forms, the star blows off enough mass that its size is significantly reduced to about the size of Earth. It is a core of carbon, a shell of helium outside that, and an outer shell of hydrogen. These small stars do not have sufficient mass for the carbon core to collapse and heat up enough for carbon fusion to occur. Eventually the white dwarf cools to a temperature too low for it to glow from thermal emission. It is then called a black dwarf—a carbon cinder, the size of Earth with the mass of a small star. We detect them only by their gravitational effect on other objects. Neutron Star More massive stars (usually more than eight times the mass of the sun but less than 25 times the mass of the sun) end in a much more spectacular way than do smaller stars. We pick up where the red giant left off, but in this case, we are looking at a much more massive star. Now there is sufficient mass that the collapse of the carbon core yields fusion to oxygen and neon. Subsequent collapse of that oxygen and neon yields fusion to silicon and sulfur, which is then followed by iron. Each time, there is a shell outside the core that does not experience renewed fusion, so the star finally resembles an onion with an outer layer of hydrogen and layers below that of successively heavier elements, up to iron, as this figure shows. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Iron, as we learned in Lesson 25, is the heaviest element that can be produced in this manner—all the heavier ones require a very large input of energy to be created by fusion of less massive elements. When fusion to iron in the core shuts down (this happens within a day of when it started —things are happening so rapidly at this stage), gravity again takes over, and the core collapses in seconds. The outer layers collapse so violently that the whole core is heated to enormous temperatures and rebounds in an explosion that releases as much energy as all the normal stars in a galaxy combined. One of the most recent nearby supernovas was detected in 1987. The photographs show before and after shots of the star. Quite a difference, huh? The energy of a supernova is great enough to fuse lighter elements into all the heavy elements (even those beyond iron in the periodic table). Our current best theory about the origin of all the chemical elements heavier than atomic number eight involves supernova explosions that have scattered the elements into interstellar space to become the raw materials for later generations of stars and planets. Supernova explosions also create supernova nebulae called supernova remnants. The Crab Nebula, shown below, is an example of a supernova remnant from a supernova that was observed in AD 1054. By the way, if you would like to see more supernova remnants, feel free to go to the Hubble Telescope image collection (Links to an external site.). You can look to your heart’s content at all the amazing supernova and star images! After the supernova explosion occurs, a substantial amount of matter is still left after the Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

outer layers have been ejected. This matter rapidly collapses gravitationally to the size of a small city. The resulting pressure is so large that the electrons and protons in the plasma are squeezed together to form neutrons. We call this a neutron star. This neutron star may have a strong magnetic field that accelerates charged particles, causing them to emit X-rays, radio waves, or visible light in searchlight-like beams. If those beams sweep past Earth’s location as the neutron star rotates, we detect them as rapid pulses and call them pulsars. The Crab Nebula contains a pulsar. As a fun side note, the emission from a pulsar is so regular and continuous that when the first one was discovered, it was semi-jokingly named LGM-1 (for little green men) as astronomers wondered what non-man made phenomenon could cause this signal. Black Holes Neutron stars are bizarre, but something even more strange happens to much more massive stars (greater than 25 times the mass of our sun). For these stars, there is no known force that can stop the collapse of the star after the supernova occurs. The gravitational force for something this massive turns out to exceed the strength of the electromagnetic force, and the star collapses until it is arbitrarily small. The gravitational force of such an object is so large that even photons cannot escape it—hence the name black hole. So if it doesn’t shine, how can we detect one? Many stars are members of gravitationally bound pairs that revolve around a common center of mass. If one of the stars of a binary pair becomes a black hole, it begins to pull gas from the other. As gas falls toward the black hole, it forms an orbiting disk around it and gradually spirals in. The charged particles spiraling into the black hole should, theoretically, emit enormous amounts of X-rays. Such emissions have been observed, and there appears to be no other explanation for them. Thus, we have “seen” black holes. Supermassive black holes are thought to be at the center of most galaxies. Additionally, while it is true that once matter and light get too close to a black hole they can’t escape, gas close to the black hole, but not too close, is also affected. Most of this matter “feeds” the black hole, but a small fraction of the matter is accelerated by the black hole’s gravitational force and magnetic fields to form jets of gas that escape the reach of the black hole. Due to the enormous energies involved, this gas moves at speeds close to the speed of light. Images taken by the Hubble Telescope and other more recent telescopes show us what these jets look like. The image below shows an example of jets escaping a black hole found in the core of the galaxy Hercules A. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

7) The energy that powers the sun’s glow is found in the core . Explanation: The temperature in the outer layers of the sun is not high enough for fusion, the energy source of the sun, to occur; While it is true that the light we see comes from the convective layer of the sun, this layer is not the source of the energy. 8) Which of the following is the fuel for the sun’s energy? Hydrogen Explanation: The sun's energy source is fusion, and since it is a small star, the type of fusion occurring is the basic beginning form of fusion. 9) Which of the following mechanisms is occurring at the sun’s core? Fusion Explanation: A star is composed of mainly hydrogen with helium and some other elements. These smaller elements do not experience fission; There are no chemical reactions that would give off enough energy to power a star. 10) Which of the following is a correct statement regarding the major source of energy for our sun? Nuclear potential energy is converted into kinetic energy. Explanation: The energy source of the sun is fusion. This involves nuclear potential energy being converted into the kinetic energy of the gasses. This kinetic energy of the gasses is thermal energy. 11) The light we see at the sun’s surface is directly due to accelerated charges. Explanation: We see the result of fusion in the core. Thermal energy from the core moves up through the layers of the sun by convection and radiation, causing the charged nuclei in the outer layers to accelerate. Do you remember what accelerating charged particles create? Think back to Lesson 11. 12) The energy of the sun reaches Earth by radiation . Explanation: There is no medium across the space between the sun and Earth, so conduction and convection cannot occur; While there certainly is distance moved between the sun and Earth, what force would be doing the work? The thought of black holes used to fill me with dread at night when I was a child. I imagined them “gobbling” up everything in their path, including our solar system and me. Back then, I did not comprehend the enormous distances of space. It still boggles the mind, but it’s gotten better. What are the distances between stars, and how are they measured? Remember back to Lesson 32, we discussed radar ranging and triangulation as methods to measure close and relatively close distances. Triangulation was the first rung on our distance ladder. Our second rung involves a brightness-distance method. In order to determine the distance to a star based on how bright the star looks, we have to be able to figure out how bright that star really is. Depending on where a star is in its life cycle, there are three different techniques. H-R Diagrams and Main Sequence Stars Most stars fall on a central band known as the main sequence, which is when the star is in its longest stage of life—the main sequence stage we discussed earlier in the lesson. A star forms and takes its place in the main sequence, with its position on the main sequence based on its temperature and brightness. It stays there until it leaves the main sequence as the star becomes a red giant. The Hertzsprung-Russell (H-R) diagram provides a way to determine the intrinsic Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

brightness or absolute luminosity (absolute brightness) of a star if one observes its color, which is easy to do if it is not too far away. The absolute brightness is compared with the apparent brightness to determine the distance. Astronomers have calibrated the H-R diagram using stars whose parallaxes have been measured, and then extended the distance ladder to about 300,000 light-years. Variable Stars Red giant stars are larger in size and brighter than main-sequence stars. This means they can be seen over larger distances. Cepheid variable stars are red giant stars where the pressure and gravity are not balanced, so the star collapses and expands. As the star changes size, the brightness of the star also changes. In the 1890s and early 1900s, an astronomer named Henrietta Leavitt discovered the brightness-period relationship for these Cepheid variable stars. The star’s oscillation time of contraction to expansion back to contraction (or vice versa) is related to the star’s size and absolute luminosity. This means if you can measure the oscillation time, which is generally over a period of a few days to a hundred days, you can determine the star’s absolute brightness and, in a manner similar to that which we previously described, compare it to the apparent brightness of the star from Earth to determine the distance of the star. The oscillation time is determined by measuring how long the oscillations in the star’s luminosity take. Cepheid variables that are also close enough to use parallax or the H- R diagram are used to calibrate this method, and the distance ladder is extended to nearby galaxies in which Cepheid variables can be spotted. In the 1920s, Edwin Hubble (for whom the Hubble Space Telescope is named) used Cepheid variable stars to gauge the distances to several galaxies. He showed without doubt that they are very far away from our own galaxy. These variable red giant stars extend the distance ladder out to about 20,000,000 light-years. Type 1A Supernovae The brightest stars ever become if they blow up in a supernova explosion. These explosions are bright enough to be detected billions of light-years away. However, for most supernovae there is no way of knowing how bright the explosion actually is. Different stars have different masses and so the stars will blow up differently. If we can’t figure out the absolute luminosity, we can’t determine distance, regardless of whether we can see the exploding star. There are, however, a few supernova explosions that are so well behaved that we know Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

exactly how bright they really are. It takes a very specific set of circumstances, so these supernovae are rare. We call these types of supernovae Type 1A supernovae. These supernovae start with two stars that formed together and orbit each other closely. Both stars must be small stars destined to become white dwarfs, but one of them is only a little too small to blow up in a supernova. Because the larger star has more mass, it has a shorter life and turns into a white dwarf first. When the smaller star becomes a red giant and expands, the white dwarf steals some material from the red giant. If the white dwarf steals enough mass, it will blow up in a supernova. Because the white dwarf had already lost its hydrogen atmosphere, the light from these supernova explosions doesn’t contain hydrogen’s characteristic emission lines, and it is easy to distinguish from other supernovae. All these supernova explosions start with a star that has the exact minimum mass needed to explode. This means they all have exactly the same brightness when they go supernova. As with the other brightness-distance techniques we have discussed, when a Type 1A supernova is detected, the apparent brightness is compared to its absolute luminosity to determine the distance to the star. The brightness-distance method using Type 1A supernovae takes us nearly to the edge of the universe with our distance ladder. We will discuss one additional distance measuring technique in the next lesson. 13) When you use the h-r diagram to find the distance to a red and a blue main sequence star, what does the diagram tell you? That the red star is dimmer. 14) How can you use the information on the h-r diagram to find the distance to a star? We can measure how much light from the star hits us and what color the star is. If we know how much light that star actually produces, then we can calculate distance, and the h-r diagram tells us how much light a star produces based on its color. Chapter 33 Quiz 1) Which of the following represents the proper sequence for the history of a massive star (a star which is not among the most massive stars but which has more mass than eight Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

times the mass of our sun and less than 25 times the mass of our sun)? protostar, main sequence, red giant, repeated cycles of expansion and contraction, supernova, neutron star 2) The sun is now in that state in which it spends most of its active life, a state which began about five billion years ago and is expected to last until about five billion years from now. According to present theory, which of the following is the energy source of the sun? the fusion of hydrogen into helium 3) The ultimate source of light energy emitted by a protostar is the conversion of gravitational potential energy to other forms of energy that indirectly give rise to light. 4) Two main sequence stars, one red and one blue, are located the same distance from the Earth. If these stars are observed, what will you see? The blue star looks brighter than the red star. 5) The gravitational force causes a protostar to collapse. Which of the following tends to offset and slow the collapse? The question refers to a time in the evolution of a protostar before it moves to the next stage and becomes a star. pressure from the motion of hot hydrogen 6) Most stars spend the greater part of their active life as a hydrogen-fusing star . 7) The sun will eventually become a white dwarf . 8) If you wanted to measure the distance to a distant galaxy, which of the following distance measurement techniques could you use? Brightness-distance relationships using type IA supernovae CHAPTER 34: COSMOLOGY: THE HISTORY OF THE UNIVERSE Introduction In this lesson we discuss objects in our universe as far as the eye (and telescope) can see. Initially, galaxies were thought merely to be other solar systems in our galaxy, but when the distances were calculated, the scale of the galaxies was amazing. To gain meaningful information about these galaxies, accurate distance measurements are necessary. We will discuss how to measure distances to other galaxies, what galaxies look like, and how our universe began. Key Terms - Barred spiral galaxy: A galaxy that is similar to a spiral galaxy except that the spiral- arms pattern originates from a bar of material that passes through the nucleus of the galaxy. - Big Bang: A cosmological model that indicates that our universe expanded from a specific moment of creation that was very hot. - Cosmology: The study of the universe and its formation. - Cosmological redshift: Galaxies that are moving away from the Milky Way and therefore have a spectrum that is shifted toward the red end of the spectrum. - Dark energy: An energy associated with the space that is causing the rate of expansion of the universe to increase with time. - Dark matter: Matter with mass that does not emit light and cannot, therefore, be seen Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

with a telescope. - Elliptical galaxy: A galaxy with an elliptical shape and little dust and gas. - Irregular galaxy: A nonsymmetric galaxy that does not have a well-defined shape like the spiral and elliptical galaxies. Irregular galaxies generally include gas, dust, and active star-forming regions. - Local Group: A small group of more than two dozen galaxies associated with our Milky Way. In addition to the Milky Way, some of the galaxies included are the Andromeda galaxy, the Large Magellanic Cloud, and the Small Magellanic Cloud. - Milky Way: The galaxy to which our solar system belongs. - Quasar: A luminous galaxy with a large red shift and starlike appearance when viewed through a telescope. - Spiral galaxy: A galaxy flattened into a disk shape with a pattern of spiral arms wound about a central nucleus. Spiral galaxies usually include dust, gas, and active regions of star formation. Use the following information to answer the next 3 questions: You may have heard of a galaxy “far, far away” but what does it mean to have a galaxy far, far away? You know from your reading that there are different types of galaxies, but let’s take a quick look at the galaxy types again. After we’ve looked at galaxies, we’ll examine the far, far away part. Spiral Galaxies The most common type of galaxy is the spiral galaxy. About 75% of all known galaxies are a type of spiral galaxy. Spiral galaxies come in two types: barred spiral galaxies and unbarred spiral galaxies. In either type of spiral galaxy, the spiral galaxy consists of a central bulge of stars of older red and yellow stars and two or more arms which rotate around the central bulge. Newer stars and forming stars are found in the spiral arms. These stars are often bright blue. Let’s have a look at some examples of spiral galaxies. Here is an example of the Whirlpool Galaxy and a small companion galaxy. This is NGC 4414, a galaxy about 60 million light years away. This is the Andromeda Galaxy—our closed spiral galaxy neighbor. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

This is an example of a barred spiral galaxy, NGC 1073. As far as astronomers can tell, our Milky Way galaxy is a barred spiral galaxy. Of course, we do not have an actual picture of our galaxy. A faint bar can be seen in this galaxy, NGC 4921. Elliptical Galaxies Elliptical galaxies are the second most common type of galaxy. Twenty percent of all galaxies are elliptical. Elliptical galaxies look like the central bulge of a spiral galaxy without the spiral arms. They come in all sizes from very large to quite small, generally have little gas and dust, and consist mainly of older red and yellow stars. This is a giant elliptical galaxy called ESO 325-G004. It is about 450 million light years away. Notice the other galaxies in the image, including the barred spiral galaxy toward the bottom of the frame. This is an elliptical galaxy called IC 2006. Irregular Galaxies The least common type of galaxy (about 5%) is known as the irregular galaxy. These galaxies don’t have a regular shape. They are just the oddball galaxies. This is the category for the non-spiral and non-elliptical galaxies. Irregular galaxies are generally smaller galaxies and are thought to often form when two galaxies collide. Often active star-forming regions are found in irregular galaxies. Sometimes, irregular galaxies are also called peculiar galaxies. There are two smaller irregular galaxies which orbit the Milky Way called the Magellanic Clouds. Here are some examples of irregular galaxies. This is an image of the Small Magellanic Cloud, one of the irregular galaxies which orbit Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

the Milky Way. This is ESO 338-4, another example of an irregular galaxy. Notice the large amount of stars being formed as determined by the blue stars. 1) After looking at the pictures of the galaxies, when you compare the pictures of spiral, elliptical, and irregular galaxies, which have the largest percentage of red and yellow stars compared to blue stars? Elliptical 2) What type of star is a younger star? Blue stars because blue stars indicate a hotter temperature and go through their hydrogen fuel more quickly. 3) Which type of galaxy has the oldest average age of stars? Elliptical Our galaxy is part of a group called the Local Group that includes about 60 galaxies, three large spiral galaxies, several irregular galaxies, and a lot of dwarf elliptical galaxies. This video gives you an idea about our part of the Local Group. VIDEO: What Is the Nearest Galaxy to the Milky Way? An important part of understanding our galaxy and universe is measuring the distances to other objects in our universe. Look at this picture: Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Notice the various objects in the picture. It’s fairly easy to locate objects on the two- dimensional image. However, determining the distances can be much harder. The lower version of the image has arrows indicating three different objects at vastly different distances. In this picture, the quasar and the star look identical, but the quasar is much, much farther away. In the previous lesson, we discussed three methods to measure the distance to objects that are very close (radar/laser ranging) to close-ish (triangulation), to farther (brightness-distance relationships). Brightness-distance methods using main sequence stars only reach tens of thousands of light years. We are able to reliably measure the distance to Cepheid variable stars tens of millions of light years away but that is nowhere near the ten billion light years we want to measure when we are looking at galaxies. Brightness-distance using type 1A supernovae can get us out to the edges of the universe. However, those supernovae are rare. We often want to know the distance to objects that haven't experienced a recent supernova. So, how do we measure these vast distances to the edges of our visible universe? This leads us to our last distance measuring method, cosmological redshift. Cosmological Redshift When Edwin Hubble used Cepheid variable stars to gauge the distances to several galaxies, he was able to show conclusively for the first time that there were stars independent of our own galaxy and far from it. Besides that, he also found something very interesting. He found that the spectra of distant galaxies were shifted toward the red end of the spectrum. The absorption spectrum for the light emitted by a galaxy is shown in Figure 34.11. Compare it to the light emitted by a star show in Figure 34.12. Notice that the absorption lines in Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

the galaxy spectrum have shifted toward the red side of the spectrum. The dark lines on these continuous spectra are absorption lines that are characteristic of the chemical elements that make up stars. The lower spectrum represents one from a typical nearby star. Hubble observed that in the spectra of distant galaxies (the upper one, for example), these lines are shifted toward the red end. At this point, you may be asking, “Yeah, so what’s the big deal?” Maybe you are thinking the shift isn’t even that big of a deal—it looks pretty small. Well, think way back to Lesson 10 when we discussed the Doppler effect. Remember that a shift in the observed frequency indicates that the source and the observer are in motion relative to each other. If the shift is toward lower frequencies (red light, in this case), the source is moving away from the observer. If the shift is toward higher frequencies (blue light, in this case), the source is moving toward the observer. Also, the faster the source moves away from the observer, the greater the shift becomes. The next activity shows the spectra of several galaxies. In it, we have used smaller galaxy shapes in a schematic way to indicate greater distance; galaxies are not all the same size. Use your mouse to click on each of the five spectra and watch the plot develop. Note the relationship between distance and the amount the spectral lines are shifted. Hubble discovered that the farther away a galaxy is, as measured using Cepheid variable stars, the faster it is receding—that is, the greater its redshift. This cosmological redshift and its linear relationship between speed and distance add another rung to our distance ladder. If we are able to measure the redshift of a galaxy, using the relationship between redshift and distance, the distance can be measured. Just a note of caution: Sometimes people think that this redshift is visible with the naked eye so that if you see a reddish star in the night sky, it’s due to redshift. That is not the case. If you see a reddish star in the night sky, it’s probably something like a red giant. Betelgeuse in the constellation Orion is an example of this. Cosmological redshift is a small change in the position of lines in the spectrum of the galaxy (or object, such as a quasar, for example). It is typically impossible to see any actual change in color. The image below shows the scope of how galaxies fit in with the rest of the universe. Also notice the distance the various distance-measuring techniques can reach. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

4) If you want to measure the distance to a nearby star, about 100 ly away, what distance measurement technique should you use. Select the best, most accurate method. If two or more would work equally well, pick them all. Triangulation 5) How would you determine the distance to a main sequence star near the edge of our own galaxy, 10,000 ly away? H-r diagram, brightness-distance 6) How would you determine the distance to a distant galaxy 50,000,000 ly away? a) Red shift b) Type 1A supernova, brightness-distance The second implication of Hubble’s distance measurements is that the redshift observed for all galaxies outside the Local Group is interpreted as evidence for an expanding universe. If galaxies were in random motion, one would expect random redshift and blueshift measurements to be taken for the various galaxies. If all the observed galaxies are moving away from us (except those twenty or so close enough to be gravitationally bound to our own galaxy in the Local Group), then one possible explanation is that we are in the center of the universe. This is not a very satisfying explanation for cosmologists because it places us in an inexplicably special place, to the exclusion of everything else. Besides, there is a much more acceptable proposition: Imagine that you are about to blow up a balloon. However, before you blow up the balloon, you decide to draw little dots all over the balloon that are uniformly distributed on it. Now you blow it up. Did you notice that the dots got farther from one another as the balloon expanded? If you were a small inhabitant on a dot and could see all the other dots, you would conclude, correctly, that all the other dots are receding from yours. Yet, no dot would be in the center of anything. The balloon just showed what happens to a single 2-D surface as it expands. Here is a visualization from the European Space Agency showing the same process in 3-D. Note that all of the galaxies throughout the 3-D space move away from each other. VIDEO: The Expanding Universe Did you notice that the galaxies got further from one another as the sphere expands? If you were a small inhabitant of one galaxy and could see all the other galaxies, you would conclude, correctly, that all the others are receding from yours. Yet, no galaxy would be in the center of anything. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

Hubble concluded from his observations that the universe, the entire fabric of space- time, is expanding and taking the galaxies with it. So, the cosmological redshift is not so much a Doppler effect as it is an expansion effect—the galaxies are not rushing away from each other but are being carried apart as space expands. Running that concept backward implies that everything in the universe began in a very small volume and then “exploded.” That explosion is termed the Big Bang, and it is the currently preferred model of cosmology because it explains very well what we observe. Not only are all the galaxies moving away, but the farthest are moving the fastest. Here is a video that runs through the last section again, complete with animated graphics to illustrate what we're talking about. VIDEO: PHY S 100 Chapter 34 | The History of the Universe 7) Doppler's equations tell us that the red-shift of a galaxy is directly related to which of the following? Speed of the galaxy (relative to the Earth) The discovery that galaxies were not only moving away from each other but were moving away with a linear relationship between their speed and the distance they had traveled implied one thing—everything started out at the same place. All of the matter and energy in the universe originated from one single point in space and time, known as a singularity. This is shown in the figure below. This implication was first realized by a graduate student by the name of Georges Lemaître in the late 1920s. He published the connection between the Hubble Law and a starting point for the universe in 1931. Initially, his work was not well received. Lemaître was an ordained Catholic priest who taught at a Catholic university and many of his contemporaries viewed his theory as a blatant attempt to impose a moment of creation on science. They began referring to his theory derisively as “The Big Bang,” and the name stuck. Religious scholars of the time, on the other hand, embraced his theory. In 1951, Pope Pius XII declared that it was scientific validation of Catholicism. Lemaître was reportedly upset by this mixing of science and religion. He said: As far as I see, such a theory [of the primeval atom] remains entirely outside any metaphysical or religious question. It leaves the materialist free to deny any transcendental Being. He may keep, for the bottom of space-time, the same attitude of mind he has been able to adopt for events occurring in non-singular places in space- time. For the believer, it removes any attempt to familiarity with God, ...It is consonant Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

with the wording of Isaiah speaking of the “Hidden God” hidden even in the beginning of the universe... When explaining his decision to become a priest and a scientist, he said: I was interested in truth from the point of view of salvation just as much as in truth from the point of view of scientific certainty. It appeared to me that there were two paths to truth, and I decided to follow both of them. His search for truth led to the Big Bang Theory, a theory which was based on observation and could be tested. Science makes progress by collecting data that can confirm or refute ideas. If the Big Bang theory were true, then the conditions in the very early universe would have been so extreme that there would still be evidence today. Leftover radiation from the initial “Bang” should fill space. Because of the expansion of the universe, the wavelength of such radiation would by now be shifted to the microwave range. In 1965, two Bell Laboratories scientists named Arno Penzias and Robert Wilson discovered, somewhat serendipitously, a faint microwave radiation apparently coming from all directions that was not of terrestrial origins. This was shown to be the predicted cosmic background radiation. Besides the predicted background radiation, the elements found in the universe should match those that would be formed during a short burst of fusion before the universe expanded and cooled. As the temperature of the universe dropped rapidly after the Big Bang, it reached a point at which protons and neutrons could form, but they still interacted with each other (and neutrinos and electrons) via the weak interaction. As the temperature continued to drop, there was a short period of time where temperatures were cold enough for stable nuclei to form but hot enough for fusion to take place. During this time, more complex nuclei could form. The Big Bang model predicts the universe to be about 25% helium and 75% hydrogen by weight. When we measure the spectra of visible matter in space where no additional fusion has taken place due to stars, we observe that composition—25% helium and 75% hydrogen. By the mid-1960’s both the existence of a cosmic microwave background radiation and Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

the expected hydrogen to helium ratio from fusion had been confirmed. At that point, the Big Bang moved from a controversial idea to the only theory that was consistent with all of the observations. None of the other models could explain how space came to be filled with microwave photons that are nearly perfectly uniform in all directions. None could explain why the gasses in interstellar space are a perfect match for the gasses that would form from hydrogen fusion taking place for a short time and then stopping. The Big Bang model was also the only model that could account for the observed relationship between speed and distance seen in cosmological redshifts. So, all of the other models were abandoned in favor of the Big Bang theory. Small details of the Big Bang theory continue to be tweaked every time new information is discovered, but at this point there is a huge body of evidence that the core idea is correct. All of the matter and energy found in the universe came into existence at the same point and time. Strangely enough, though, as scientists became more and more accepting of the theory, the religious community became less enthusiastic. Some religious scholars began to regard the Big Bang theory as an attempt by scientists to explain away the existence of God. Today, when the term “Big Bang” is used derisively, it is almost always by a religious non-scientist. This leaves those of us who are both religious and scientists shaking our heads in confusion. To summarize the Big Bang theory, the universe began as a great amount of pure energy concentrated into a tiny space. This energy, and space, too, expanded and cooled into matter, eventually ending up with the universe, galaxies, solar systems, and all that we have today. It brings to my mind a quote about physics fashion that has been attributed to Einstein: Once you can accept the universe as something expanding into an infinite nothing which is something, wearing stripes with plaid is easy. 8) What is Cosmic Microwave Background? Leftover photons from shortly after the formation of the universe that have been stretched to really long wavelengths as the universe expanded. Stripes and plaid aside, there are a few questions for which the Big Bang theory doesn’t provide answers, yet. Missing Mass The Big Bang theory explains the present state of the universe as arising from an initial catastrophic explosion. Understanding the future of the universe depends on knowing some things that have not yet been determined with certainty. If there were sufficient mass in the universe, then the total gravitational attraction would be sufficient to eventually stop the expansion and begin a contraction. This type of universe is called a closed universe. If the universe were closed, then it would eventually collapse to the volume it occupied at the time of the Big Bang. This has been called a “Big Crunch,” and assuming that it resulted in another Big Bang, we would then be living in an oscillating universe—one that cycled between big bangs and big crunches. This model appealed to scientists because it provides a nice self-contained package. But all the current experimental evidence points to a second option. If there is less than the amount of mass required to close the universe, we then live in an open universe that will expand forever. There isn’t anywhere near enough matter that we can Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

see (because it emits light) to close the universe. There is good evidence to indicate that a mysterious form of dark matter we have not yet identified exists, but that still isn’t enough matter to close the universe. Current evidence suggests that the universe is precariously balanced just short of closed. That is, it will expand forever and will not collapse. Missing Energy Because of gravity, cosmologists used to think that the rate of expansion would continue to slow with time, but it appears now that the expansion of the universe is actually speeding up. Besides looking for dark matter, astronomers are looking for dark energy—the energy that drives the extra repulsion and increasing rate of expansion of the universe. Like the early models of the atom that underwent many refinements as more information was discovered, scientists are continually testing and improving the Big Bang theory. Parts of the theory are well established and supported, but there are plenty of unanswered questions. The chance to find a few of the missing pieces of the puzzle and put them in place is what makes scientists tick. With that said, let’s end with a Calvin and Hobbes cartoon. 9) What is "Dark Matter"? No one knows. That's why this sections was called "unanswered questions" Chapter 34 Quiz 1) When the absorption spectrum of light from distant galaxies is measured, what is found? The lines in the absorption spectrum are shifted towards the red end of the spectrum, with light from the most distant galaxies being shifted by the largest amount. 2) Spiral galaxies typically contain large numbers of blue stars and bright nebulae, while elliptical galaxies typically contain mostly yellow and red stars. What can you conclude based on this information? Spiral galaxies are actively forming new stars, while elliptical galaxies have little or no star formation going on. 3) What would be the best method to determine the distance to a distant star about 100,000 light years away in our own galaxy? Measure its color and apparent brightness, then look on a H-R diagram to determine its absolute luminosity. Then compare absolute luminosity and apparent brightness to determine distance. 4) Which statement is true in the Big Bang model? The microwave background radiation that fills the universe is left over from the early stages of the expansion process. 5) It appears that the expansion rate of the universe is increasing with time. TRUE 6) When measuring the positions of the lines in the absorption spectrum of stars in a Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

certain galaxy, the lines are all shifted toward the blue end of the spectrum. This means the galaxy is moving toward the Earth . 7) Which of the following is true about our galaxy in relation to the rest of the universe? There are a few dozen close galaxies that are moving towards the Milky Way or orbiting around it, but the rest of the galaxies are moving away. 8) What type of galaxy is the Milky Way? A spiral galaxy Chapter 34 Homework 1) You have a galaxy that is too far away to see individual stars, but you can see a little smudge of light from the galaxy. What would be the best way to find the distance to this galaxy? a) Red shift b) Type 1A supernova, brightness-distance 2) You have two distant main sequence stars, a red star and blue star, both over 100,000 ly away. The red star appears brighter than the blue star. What can you conclude about their distance? A) The red star is closer 3) You have two distant main sequence stars, a red star and blue star, both over 100,000 ly away. The red star appears brighter than the blue star. What would be the best way to find the distance to these stars? E) H-r diagram, brightness-distance 4) You have a spiral and elliptical galaxy that are close enough that you can barely resolve the very brightest red-giant stars as individual points. These stars vary in brightness with a regular frequency. Stars with the same frequency are brighter in the spiral galaxy. What can you conclude about their distance? A) The spiral galaxy is closer 5) What would be the best way to find the distance to these galaxies in the previous question? D) Cepheid variables 6) You have two nearby main sequence stars, a red star and blue star. They’re both within 1000 light years of our sun and the blue star appears brighter than the red star. C) You can't tell from the information given. You'd need to do the math and calculate the distances. 7) What would be the best way to find the distance to these stars in the previous question? C) Triangulation 8) You are observing a galaxy that suddenly got twice as bright and you detect the light curve for a white dwarf that stole enough mass from a companion star and went supernova. What would be the best way to find the distance to this galaxy? F) Type 1A supernova, brightness-distance 9) How can you measure the mass of something you can barely see? C) Measure the orbital radius and speed of something orbiting the object 10) What are the evidences that support the Big Bang theory? a) Cosmological red-shift b) Microwave background radiation c) Hydrogen-Helium ratios 11) When we measure the spectra of stars from distant galaxies, the lines are shifted towards the lower frequency, longer wavelength end of the spectrum. The more distant the galaxy, as measured by brightness-distance methods, the larger the shift. This is Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

evidence for the big bang. Why? C) The amount of shift is an indication of speed. A direct relationship between distance and speed means everything started at the same place at the same time. F) The universe is still expanding, stretching the photon wavelengths along with everything else. The farther away a galaxy is, the more time it takes for the light to get to us, and the more the photon will be stretched. 12) No matter what direction we look, there is a nearly uniform low frequency radiation hitting us from all directions in space. This is evidence for the big bang. Why? A) The big bang should have resulted in a lot of radiation that would have been stretched to long wavelengths as the universe expanded. 13) Interstellar gas is a mix of 25% He, 75% H, and trace amounts of Li with almost no heavier elements. This is evidence for the big bang. Why? E) Because that's the mix of elements you'd expect if you started with a container of hydrogen and had temperatures hot enough for fusion for a short time, but then rapidly cooled it so the fusion stopped. PRACTICE EXAM 4 1) The forces opposing the expansion of the universe are due to the gravitational interaction . 2) The speed of plate motion in the tectonic system is approximately 1–10 centimeters per year . 3) The cosmological red shift seems to indicate that other galaxies are moving away from the Milky Way galaxy with those farthest away moving the fastest . 4) There are four major types of studies used to determine the structure and composition of the earth’s interior. Which of these is not one of the four types? relative dating based on erosion and deposition patterns 5) The distance to galaxies very far from our own can best be estimated using the cosmological redshift . 6) What do we call a gas which transmits higher energy visible photons but absorbs a large fraction of infrared photons? Greenhouse gas 7) The major source of all surface water on the continents is precipitation . 8) Elements heavier than iron on the Earth are produced in supernova explosions . In this cross section, A is an igneous rock formation radiometrically dated at 37 million years, and C is an igneous rock formation radiometrically dated at 24 million years. E is a fault. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

The next five questions ask you to use the principles of relative dating to come to conclusions about the rock layers. 9) The rock layers labeled B are tilted and folded. Which of these is the best possible explanation as to why? The crust moved after they were deposited, tilting and folding them . 10) If you put the items depicted in the cross-section in order from oldest to youngest, which of these is the correct order? You can’t tell what's youngest; more than one of these sequences could be correct. 11) Which principle of relative dating allows you to determine the relative age of formations C and D in the cross-section? Cross cutting 12) Rock C is dated at 25 million years old. How could that date have been determined? by counting the number of microscopic cracks formed by fission products 13) Rock C is 25 million years old. What does this age represent? when the rock solidified 14) The lower mantle of the earth (the mesosphere) is thought to be mostly in what state? Solid 15) Part of the upper mantle, called the asthenosphere, is unique because most of its material is near the melting point . 16) What is the most important erosional agent of the hydrologic system? running water 17) The force(s) causing a protostar to collapse is/are gravitational force . 18) According to the Big Bang model, how do the temperature, density and structures found very early in the universe compare to those now? The earliest stages have higher temperatures, higher densities, fundamental particles (quarks and electrons) . 19) When measuring the positions of the lines in the absorption spectrum of a certain star, the lines are all shifted toward the red end of the spectrum. What does this mean? The star is getting farther away from the earth 20) The Himalayan Mountains (indicated by the black star on this map) are at the northern edge of the Indian plate. North 21) The Hawaiian islands are a linear island chain in the middle of the pacific ocean. While all of the islands are volcanic in origin, the only active volcanoes are on the largest island. What is the most likely cause for this island chain? a hot spot 22) Which of these features would you expect to find at a converging plate boundary Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

between two continental plates? more than one of these 23) Information from fossils would most likely be useful to do which of these? determining relative ages of sedimentary layers Refer to this picture as you answer the next two questions. 24) What feature does the picture show? an alluvial fan 25) Which of these caused the feature? running water 26) Which of these statements about streams is true? Streams carry more sediment when moving quickly since the stream has more kinetic energy which is used to carry more sediment 27) What happens when water subducted during plate tectonics chemically combines with the surrounding rock? The rock melts more easily 28) Most stars spend the greater part of their active life as what? hydrogen-burning stars 29) Which of these statements correctly describes how energy from the sun drives the hydrologic cycle on Earth? The energy from the sun is transferred by radiation through the atmosphere to the oceans. This radiation is strongest near the equator, and most evaporation occurs there 30) This graph shows variations in temperature over the last 400 thousand years. Based on the natural cycles in the graph, what would you predict the climate will do in the future? The climate will cool off, but in about 100,000 years it will warm back up again. Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

UNIT 4 VOCABULARY QUIZ 1) . 2) Match the astronomical distance measuring techniques with their approximate ranges. a) radar ranging - distances within the solar system b) Triangulation - distances up to about 1000 light years 3) What hydrologic feature causes deltas? running water In this picture, each of the earth’s mechanical layers is indicated with a letter & an arrow. 4) Which layer is the lithosphere? E 5) Which layer is the mesosphere? C 6) Which chemical layer of the Earth has a composition of peridotite and dense oxides? Mantle 7) Which mechanical layer of the Earth is completely solid? More than one of these a) Lithosphere b) Inner Core 8) Which mechanical layer of the Earth is completely liquid? Outer Core 9) Which mechanical layer of the Earth is mostly plastic solid with a small percent molten material? Asthenosphere 10) Match each stage in the life of a star with the size of the star. a) black hole - large (more than 10 times the size of our sun) b) planetary nebula - small (about the size of our sun) c) red giant - all stars go through this stage d) supernova - medium and large, but not small stars 11) When you arrange the following stages in the life of a certain star in order, which of these appears third? a) hydrogen-burning star b) neutron star c) Protostar d) red giant e) supernova 12) When you arrange the stages in the life of a certain star in order, which of these lasts the longest? hydrogen-burning star 13) Which of these is an accurate description of the principle of original horizontality? Rock layers become tilted or buckled and folded after the layers were originally formed Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

14) Which of these is an accurate description of the principle of cross cutting? A younger layer slices through older surrounding layers. 15) When water chemically combines with surrounding rock in subduction zones, what happens to the melting temperature of that rock? It gets lower 16) Match each rock with its rock classification. a) basalt - igneous b) granite - igneous c) limestone - sedimentary d) marble - metamorphic 17) Which of these is a method to find the absolute age of geologic events? Radiometric dating 18) The age of the Earth is approximately 4.6 billion years. This is an example of an absolute age . 19) Greenhouse gasses change how the Earth transfers heat back out into space. Which of these methods of heat transfer do they affect? Radiation 20) What two characteristics are plotted on an H-R diagram? Select both. a) Color b) True brightness 21) Which of these is an important part of the process driving plate tectonics? gravitational potential energy 22) P-waves cannot travel through the liquid outer core of the earth. FALSE 23) Fast-moving water can carry more sediment than slow moving water. TRUE UNIT 4 EXAM TA REVIEW Evidence Supporting the Big Bang EVERY SINGLE ONE OF THESE PROBLEMS IS WRONG, BUT THEY SOUND RIGHT IF YOU’RE LOOKING FOR KEYWORDS 1) Everything is moving away with the smallest galaxies moving the fastest. 2) The universe is full of high energy gamma rays left over from the big bang. 3) Heavy elements like uranium and gold could only have been found during a super explosion like the big bang. THESE ARE THE CORRECT ANSWERS. PLEASE MAKE SURE THAT YOU ARE UNDERSTANDING THE QUESTIONS AND THE ANSWERS THAT YOU ARE GIVING 1) Everything is moving away with the farthest galaxies moving the fastest. 2) The universe is full of low energy microwaves left over from the big bang. 3) The ratio of the light elements that make up the interstellar gas, hydrogen, helium, and lithium, is consistent with fusion happening for a very short period of time EARTH’S INTERIOR Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411

What is the makeup of the earth? Digging: - We’ve only dug 7.5 miles while Earth’s radius is 4000 miles Meteorites: - Earth made up of same material found in solar system - Meteorites coming from pre-existing planet/moon - 80% made of silicates and 20% made of iron (Earth is probably the same) Seismic Waves: - Shadow zones and refraction of waves coming from earthquakes Downloaded by Mary Williams (dsonnet273@gmail.com) lOMoARcPSD|37566411