GEOL Test 2 Review - Geological Time
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GEOL 1101 – The Dynamic Earth = Review Questions for Lecture Test 2
Topic 11 – Geologic Time and Dating
1.
Who wrote Natural History? When was Natural History written? How many volumes of Natural History were devoted to geology?
●
Pliny the Elder (a Roman) wrote Natural History in 77 AD. Geology is discussed in 5 of the 37 books → he provided insights into the mineral industry of Roman times, Earth materials for colour and Pliny the Elder (a Roman) wrote Natural History in 77 AD. Geology is discussed in 5 of the 37 books → he provided insights into the mineral industry of Roman
times, Earth materials for colour and ceramics, gemstones, and much more.ceramics, gemstones, and much more.
2.
Nicolas Steno is considered to be one of the forefathers of modern geological science. What principles of stratigraphy did Steno propose? List and describe each of these principles.
Principle of Superposition:
oldest strata lie at the bottom of a stratigraphic succession, youngest rocks are found at the top of a stratigraphic succession.
Principles of Original Horizontality and Continuity:
all rocks were originally deposited horizontally under the action of gravity, and continue laterally in all directions.
Principle of Inclusions:
all rock fragments that are found within a stratigraphic layer must be older than the stratigraphic layer itself.
Principle of Cross - cutting Relationships:
the geological feature that cuts across another geological feature is the younger of the two
features.
3.
Explain the premise of catastrophism. Who proposed catastrophism as a viable explanation for the origins of the Earth’s landscapes? What else was this person famous for?
Georges Cuvier (1769 - 1832) – The First Catastrophist
●
Catastrophism is a hypothesis that states that Earth’s history
can be explained by a series of supernaturally derived
catastrophes (specifically floods!). ●
Catastrophism was a very popular hypothesis for many years.
It fit in with the dominant religion of the day, and many people
had experienced catastrophes.
●
Georges Cuvier
was the first person to propose the
phenomenon of extinction in 1796.
●
He also recognized that fossil-bearing strata represented
successive assemblages of organisms.
●
This is now known as the Principle of Faunal Succession.
Cuvier’s Commentary on Human Origins
●
Homo diluvii (right image) was thought to be the remains of the
miserable sinners who perished during the Great Deluge
(Scheuchzer, 1726).
●
Cuvier conclusively showed that it was not a hominid, but rather a large salamander known as Andrias
●
scheuchzeri.
4.
What geological concept did James Hutton propose? Explain what this concept entails.
James Hutton (1726-1797) – The Father of Uniformitarianism
●
Uniformitarianism: Present geological processes have been operating throughout Earth’s history, and
can be used to explain past processes.
●
Hutton infuriated catastrophists because he believed that the Earth was hundreds of millions of years old!
Hutton recognized that the following events must have occurred at Siccar Point:
●
The older rocks were deformed by some great force (he couldn’t fully explain it)
●
The older rocks were subsequently eroded, and then younger units were deposited next
5.
James Hutton spent a lot of time staring at a rock outcrop at Siccar Point in Scotland. What geological feature is preserved at this outcrop? What is its significance?
Hutton and Unconformities
Hutton recognized that the following events must have occurred at Siccar Point:
●
The older rocks were deformed by some great force (he couldn’t fully explain it)
●
The older rocks were subsequently eroded, and then younger units were deposited next
Angular unconformity
Disconformity
Nonconformity
What kind of unconformity is present at Siccar Point?
6.
What was Charles Lyell’s main contribution to geosciences? What other scientists were inspired by his work?
Sir Charles Lyell (1797-1875) – Promoter of Uniformitarianism
●
Lyell was the person who convinced the majority of geologists that uniformitarianism was no joke. He did this using his 3 - volume work called Principles of Geology (1830-1833).
●
Lyell believed in a steady-state Earth–in other words, rocks, processes, and organisms have always existed throughout geological time (and have not changed very much).
Principles of Geology (1830 - 1833)
●
Lyell’s Principles of Geology, which built on his own work and the concepts of Hutton, changed everything in terms of how we understand the Earth.
●
However, this was only just the beginning of the geological revolution, and the next wave of scientists, which included William Smith, Sydney Savory Buckman and Johannes Walther, were just getting started.
7.
What was William Smith’s main contribution to the geosciences? Is his contribution still used today?
William Smith (1769 - 1839) – The First Geological Mapmaker
●
William Smith was an English civil engineer that independently stumbled upon
Steno’s Principle of Superposition. Smith’s main objective was to locate coal.
However, in doing so, he realised that fossils in rocks tended to follow the Principle
of Superposition as well (Principle of Faunal Succession).
●
Additionally, Smith discovered that groups of fossils
are consistent from area to
area, and are unique through time.
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Correlating Fossils from Place to Place oldest youngest
●
Sedimentary rock types may change from one column to the next, but the fossils are the same depending on the time that the sediments were deposited.
●
William Smith looked at fossil groups all over England and Wales!
William Smith’s Stratigraphic Column
Through his work, Smith was able to create a stratigraphic column. Geologists use stratigraphic columns to keep track of different rock formations.
Rock formations are commonly ordered from oldest
to youngest.
The First “True” Geological Map
●
William Smith created the first geological map of Great Britain in 1815. The map was based on the Principle of Superposition and the Principle of Faunal Succession. 8.
What geological units did Sydney Savory Buckman work on? What did Buckman’s work on these units reveal?
Advances in Relative Dating: The Contributions of Sydney Savory Buckman
●
Sydney Savory Buckman (1860-1929) followed in Smith’s footsteps. Buckman was primarily interested in trying to find fossil assemblages that represented the shortest amount of time possible.
●
Buckman’s initial research largely focused on the classification of ammonites. To characterise ammonites, he spent a great deal of time documenting the Oxford Clay.
●
Buckman’s work on the Oxford Clay revealed that there were notable gaps in the stratigraphic record associated with the unit. What could that mean?
9.
What is Johannes Walther’s Law? How does his law help to explain the stratigraphic patterns that we see?
Johannes Walther (1860-1937): The Father of Modern Stratigraphy
●
Building off of the work of Georges Cuvier
and Sydney Savory Buckman
, Johannes Walther began
to look closely at relationships between sedimentary facies that sit near each other.
●
Walther’s Law:
“The various deposits of the same facies-area* and similarly the sum of the rocks of different facies-areas are formed beside each other in space, though in a cross section we see them lying on top of each other.
(AI explained) Walther's Law basically says that layers of rock formed in different environments, like a beach or a riverbed, can end up stacked on top of each other over time. Imagine if you took a slice through
the Earth's crust and looked at the layers side by side. Even though they were formed in different places, they might look like they're all on top of each other in that slice. It's like seeing a bunch of different layers of
cake stacked up neatly on a plate. Each layer represents a different environment where the rock formed, but they all end up next to each other in the slice.
*"Facies-area"
refers to a specific geological term used to describe a particular type of rock or sediment that forms under similar environmental conditions. Essentially, it's a distinct area or region where the rock layers share common characteristics in terms of their composition, structure, and the processes that formed them. These areas can vary widely, from the seafloor to desert sands, and each one leaves its own
unique imprint in the geological record.
●
As with biotypes, it is a basic statement of far reaching significance that only those facies and facies - areas can be superimposed primarily which can be observed beside each other at the present time.”
This statement is saying that in geology, when we look at different types of rocks or sediments (facies) and
the areas where they form (facies-areas), we can only accurately compare or stack them on top of each other if they currently exist side by side in the present. In other words, to understand the geological history of an area, we should observe and compare the rocks and formations that are found together today, rather
than trying to stack rocks that are not currently existing in close proximity. This helps geologists make more accurate interpretations of the Earth's history based on the relationships between different types of rocks and their current locations.
●
What does this actually look like in a cross-sectional view?
10. What is a facies? How does it differ from a sequence?
Facies Boundaries in Stratigraphy
●
Picture yourself standing on a beach next to the ocean.
●
We know that the waves come towards us, and then recede back into the ocean.
●
Are there longer-term advances and regressions that we can document in the geological record? The answer is YES.
●
Walther’s Law allows us to recognize transgressions (i.e., sea-level rise) and regressions (i.e., sea-
level fall) by looking at facies relationships through time and space.
●
Facies:
A body of rock with specified characteristics which can be found in one or a series of areas on Earth.
●
Sequence:
A package of genetically-related facies that correlate with a transgressive or regressive cycle.
●
The two definitions above are critical elements of sequence stratigraphy!
11. Name all of the eons on the geological time scale in order from oldest to youngest.
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Hadean, Archean, Proterozoic, Phanerozoic, Phanerozoic, which means "visible life.
Collectively, the Hadean, Archean, and Proterozoic are sometimes informally referred to as the "Precambrian." The Cambrian period defines the beginning of the Phanerozoic eon; so, all rocks older than the Cambrian are Pre
cambrian in age.)
12. Name all of the periods during the Paleozoic, Mesozoic, and Cenozoic eras in order from oldest to youngest.
Paleozoic (“old life”) - - Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian
Mesozoic (“middle life”) - Cretaceous, Jurassic, Triassic
Cenozoic (“new life”) - Tertiary, Quaternary (not sure why the graphic on slide 27 of Topic 11 does not show the Paleogene.
13. What is chronometric dating? How does it differ from relative dating?
Chronometric dates are numerical values that can help us quantify geological processes
●
Dates are commonly given in ka (1000s of years), Ma (millions of years), or Ga (billions of years) → the nomenclature used depends on the isotopic system
To perform chronometric dating, we must make a few assumptions:
●
The decay constant (λ, lambda)
of certain radioactive isotopes must be known
●
Rates of radioactive decay have been constant over geological time
●
Isotopic systems are closed
(parent/child isotopes are not lost to surroundings)
14. What isotopes are useful for dating geologically young materials? What isotopes are useful for dating geologically old materials?
Radioactive Isotopes
Different radioactive isotopes are useful for different purposes. WHY?
●
Radioactive isotopes have different effective dating ranges:
●
Carbon-14 is useful for “young” materials that are <50,000 years old
●
U-Pb dating with U-238 is useful for “old” materials because its half-life is 4.5 billion years old!
15. What is half - life (aside from being an influential computer game)?
Radioactive Decay
●
Half-life refers to the time that it takes for half
of the parent isotope atoms in a sample to
decay to form atoms of the daughter (or
child) isotope
●
Both types of isotopes are often referred to
as radiogenic isotopes
16. What is the half - life of uranium - 238?
●
U-Pb dating with U-238 is useful for “old” materials because its half-life is 4.5 billion years old!
17. Where do the chronometric ages on the geological time scale come from?
Introduction to Zircon Geochronology
●
One mineral commonly used for chronometric dating is zircon (ZrSiO4).
●
Zircon is harder than quartz, and incorporates various U isotopes into its structure. This makes it an ideal mineral for U-Pb dating of old rocks.
●
Uranium-238 (
238
U) decays to form Lead-206 (206
Pb). The half-life of 238
U is 4.47 Ga, or 4,470,000,000 years.