Plate Tectonics and Google Earth

Introduction to Plate Tectonics using Google Earth Adapted from Goodell, L. (2013). Using Google Earth to Explore Plate Tectonics. In Pedagogy in Action . Retrieved N ovember 5, 2016, from http://serc.carleton.edu/sp/library/google_earth/examples/49004.html Record your answers in a Word (or equivalent) document and submit to Plate Tectonics in the Assigments tab in Sakai . Need some help with the calculations in this Assignment? Check out The Math You Need When You Need It Website for math tutorials specific to introductory geoscience courses. I N TRODUCTIO N Plate tectonics is a unifying framework for understanding the dynamic geology of the Earth. The theory suggests that the outermost layers of the Earth (the crust and uppermost mantle) make up the brittle lithosphere of the Earth. The lithosphere is broken up into a number of thin plates , which move on top of the asthenosphere (middle mantle). The asthenosphere is solid, but flows plastically over long periods of geologic time. Plate interiors are relatively stable, and most of the tectonic action (earthquakes, volcanism) takes place where plates meet – where they collide at convergent boundaries , move away from one another at divergent boundaries , or slide past one another at transform boundaries . Two informative websites that you may want to visit as you work on this assignment include: 1. The Paleomap Project by Christopher Scotese , which includes reconstructed maps to show plate locations through geologic time. 2. UCMP/Berkley Plate Tectonics webpage , where the authors have created animations of the moving plates based on the Scotese maps. But how do we define plates and plate boundaries? On what are plate reconstructions and animations based? How do we know plates are moving, how can we track their positions in the past, and how can we predict their positions in the future? To answer these questions, this laboratory assignment guides you through an examination of patterns on Earth – the topography of the earth’s surface above sea level, the bathymetry of the ocean floor below sea level, and the distribution of earthquakes and volcanic rock ages. You’ll then use geologic data to determine long-term average plate motions. To do this, you’ll use the program Google Earth, and Google Earth layers compiled from various sources. Getting started with Google Earth • On your computer, install the latest version of Google Earth from http://earth.google.com/ (this is a FREE download). • Once installed, open the View menu. Go ahead and experiment with the options, but in general you should just have the Tool Bar , Side Bar and Status Bar checked. Also on the View menu, hover over Navigation and you will see several options for the compass arrow and slide bars in the upper right corner of the Google Earth screen. “ Automatically ” is a good choice as it leaves a ghost of the image visible until you hover over it.

• Copy and paste http://serc.carleton.edu/sp/library/google_earth/examples/49004.html into you browser and then scroll down to Description and Teaching Materials then go to DynamicEarth.kmz and click on it. It should download onto your computer. Open it up and it should take you to GE and on the left side in the “Temporary Places” section of the “Places” tab. DynamicEarth.kmz will now be available every time you open GE on this particular computer. When you exit, GE should save “My Places” for the next time. But you should manually save “My Places” whenever you make significant changes to it, as GE does not autosave during a session. Okay, with an active Internet connection, you now have an interactive view of the earth! Take some time to explore the Earth with Google Earth and figure out how the navigation works using the keyboard, your touch pad (if you have one), and your mouse. For example: ▪ Zoom in and out, move N, S, E, W, grab and spin the globe, etc. The resolution will change as you zoom. Clicking on the “N” of the navigation compass reorients the view so north is “up.” ▪ At top left, “search” (and fly to) any place of interest. Zoom in and click on the “street view” icon (orange stick figure under the compass at top right) to explore an area as if you were on foot ▪ Zoom in to see individual buildings, roads, cars, etc. (For example, find the crew team and motorboat on Lake Carnegie) ▪ Go 3D! Zoom into a significant topographic feature (e.g. Mount Everest, the Grand Canyon, Niagara Falls). Hold the Shift key down and tilt the terrain using the Up/Down arrows on your keyboard to tilt the terrain, and spin the terrain using the Right/Left buttons. Do the same thing for topographic features on the ocean floor. Note that under Tools/Options/3D View you can increase the vertical exaggeration by up to 3x. This is useful to emphasize subtle features, but is pretty scary when you look at the Grand Canyon that way! ▪ On the Google Earth tool bar, click the clock-with-an-arrow icon to explore historical imagery in an area of interest (views through time of the Aims Community College campus, for example). A slider bar will pop up near the top of the image – explore different images of campus through time. When you are done, make sure to ‘unclick’ this button. ▪ By clicking and dragging, you can move things that you have found and want to save, from the “Search” menu into “My Places.” You can also re-organize “My Places” by adding and deleting items, changing the order of things, making subfolders, etc. ▪ Explore the built-in items under the Layers menu at bottom left, and Dynamic Earth layers in your Places menu. Expand and contract the folders and subfolders, turn various items on and off, etc. For example, with the Dynamic Earth/ Volcanoes of the World layer displayed, right-clicking on a volcano brings up an information box about it. Using Google Earth to examine topography

Navigate in Google Earth such that you are looking at the Atlantic Ocean, between North America/South America and Europe/Africa. Note that the deepest part of this ocean basin is not in the middle; instead there is an underwater mountain range that runs down the middle of the ocean. 1. Features like this are called mid-ocean ridges or spreading ridges. Zoom in enough to see that although the ridge is a topographic high, it also has a valley (the “rift valley”) running along the middle of it. Move your curser over the mid-ocean ridge where it crosses the Tropic of Cancer (23.5° North latitude) between North America and Africa. Report the range of elevations (in meters below sea level) of some of the highest points (shallowest water) along the mid-ocean ridge at this latitude (elevations are noted in the bottom right hand side of your screen, along with latitude and longitude. If you are zoomed out too far, the elevation won’t be reported – try zooming in a bit. Negative elevations are elevation below sea level, positive elevations are elevations above sea level). 3,340.608 meters 2. Scan around to see the other mid-ocean ridges in the Indian, Pacific and Southern Oceans . Based on bathymetry, report where you think you see mid-ocean ridges occurring in those oceans. Are they in the middle or somewhere else? Be specific in your description of location.

Return to your view of the Atlantic Ocean and click on the ‘Plate Boundary Model’ layer (click the box to show it and then click the + or arrow to expand the legend). This shows plate boundaries and the names of major plates. Also, click on ‘Seismicity’ and choose the ‘20 years of large earthquakes’ layer. 3. Where is the plate boundary located that separates the South American and African Plates ? (Give approximate latitude N and S of the boundary along the mid ocean ridge) 0°17’44.25 N and 23°32’35.27 4. If the plate boundary was not shown, how might you use the location of earthquakes and seafloor topography to determine its location ? The earthquakes run along the edges of the tectonic plates. Now, click the on the ‘Seafloor Age’ layer. The “Seafloor age” layer shows the ages of volcanic rocks that have erupted and cooled to form the ocean floor. Focus on the Atlantic Ocean. Note that the age bands generally run parallel to the spreading ridges. Seafloor age is a critical piece of evidence for plate tectonics; these are used to reconstruct how ocean basins have developed over time and predict how they may evolve in the future. 5. How many years does each colored band represent? 10 million years 6. On average, continental crust is 2 billion years old; the oldest rocks are 3.8 billion years old, and some of the grains in those rocks are even older. (a) What is the age of the oldest seafloor? 180 Million years old (b) On average, which is oldest – the continents or the ocean basins? The continents 7. In general, where do you find the youngest seafloor in the Atlantic basin? The oldest? The youngest is usually towards the center of the ocean and the oldest is along the edges of the continents. 8. Focus on the northern Atlantic Ocean, near the east coast of the US and the northwest coast of Africa. How long ago did the northern Atlantic Ocean begin to open up or start spreading? Describe your reasoning. 170-180 Ma because among the edges of Africa and the US is a brighter purple color. 9. Based on your understanding of plate tectonics, what type of plate boundary forms a mid- ocean ridge? Divergent plate boundaries 10. Is oceanic crust being created or destroyed at this plate boundary (and other mid-ocean ridges)? Created

15. Navigate Google Earth to west of South America such that you can see the Nazca Plate, located just east of the East Pacific Rise (the boundary between the Pacific Plate and the Nazca Plate). Focus on the seafloor just west of South America. N otice the deep blue colors parallel to the coastline – these indicate very deep depths. How far off the coastline (on average) is this deep feature? Zoom in closely and, moving your mouse across these deepest depths, report the maximum depth of this deep feature where it crosses the Tropic of Capricorn (about 23° South latitude). 10,712 feet/ 4.9 miles/7.9 Km These deep linear features, the lowest points on Earth, are called ocean trenches . 16. Based on your understanding of plate tectonics, identify what type of plate boundary forms an ocean trench. Is oceanic crust formed or destroyed here? Convergent plate boundaries, destroyed. 17. Knowing that the western boundary of the Nazca Plate is a divergent boundary known as the East Pacific Rise, where would you expect to find the oldest seafloor on the N azca plate? Explain your answer. 18. Locate the chain of islands in the center of the Nazca Plate. These are the Easter Island Hot Spot Chain. (a) Using the same method that you used in Questions 12-14, calculate the rate of movement of the N azca Plate in cm/year. (b) Determine its direction of movement. 2,776.56km/25.17ma= 110.31 19. Is the East Pacific Rise spreading faster or slower than the mid-Atlantic Ridge? Faster 20. Do you think that the N azca Plate is getting smaller, larger or staying about the same size over time? Explain your reasoning. Smaller because it’s oceanic crust is being destroyed at the convergent plate boundaries.