Plate Tectonics Review via Google Earth

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Middle Tennessee State University *

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1030_002

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Geology

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Dec 6, 2023

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Plate Tectonics Review via Google Earth Due October 2 Plate tectonics is a unifying framework for understanding the dynamic geology of the Earth. The theory posits 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 geologic time scales. 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. Reconstructions of the Earth’s tectonic plate locations through time are available, for example, at: http://www.ig.utexas.edu/research/projects/plates/recons.htm#movies http://www.scotese.com/newpage13.htm http://www.ucmp.berkeley.edu/geology/tectonics.html 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 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. A. Getting started with Google Earth  On your computer, install the latest version of Google Earth from http://earth.google.com/  Once installed, open Google Earth, under the Tools/Options/3D View/ menu choose the “ Decimal Degrees ” and Meters Kilometers ” options and makes sure the “ Show Terrain ” box is checked.  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.  Load the DynamicEarth.kmz file (found on our D2L page under Content/Plate Tectonics) into GE. You should be able to double-click on the filename and it will open within GE. Or, you can download the file onto your computer, and open it in GE by using File/Open and navigating to the file. Once the DynamicEarth.kmz is loaded, click and drag to move it from “Temporary Places” to “My Places.” Then save “My Places” by clicking File/Save/Save My Places. 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 Google Earth does not autosave during a session. Ok, 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, 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. (Find MTSU or your house/apartment.)  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 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 Princeton campus, for example)  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. 1. Find something interesting, significant, cool, etc. to share on Google Earth with your classmates in our class session. This can even be something that other people have developed – if you want to spend some time poking around on the web to see what others have found. Feel free to include more than one. Give a brief description of your item(s) below: - TexasGulf Potash Ponds - 38°29’0.16″N 109°40’52.80″W - These are Potash harvesting ponds near Moab - The ponds are dyed blue to increase evaporation to harvest the potash.

B. Topographic Patterns Uncheck all of the layers, except the plate boundaries, and focus on topographic features of the earth. Topography of the earth ABOVE sea level 2. Are mountains randomly distributed on the continents, or do they tend to occur in particular patterns (clusters, linear chains, arcs, etc.)? - Mountain ranges occur in particular distribution patterns that correlate with plate tectonics. They indicate where continents underwent collision and orogeny, and eventually rifted apart. 3. Find Mt. Everest, the highest point on earth. Zoom in enough to see the summit, then pan your cursor around to locate the highest point (elevations shows up in the status bar at the bottom, as long as View/Status Bar is selected): 8756 meters Topography of the earth BELOW sea level We are all relatively familiar with the topography of the Earth’s surface above sea level, but less so with the bathymetry of the Earth below sea level. Before this was known, most people assumed that the seafloor was relatively flat and featureless, and personal experience with lakes and rivers suggested that the deepest part would be in the middle. Actual mapping of the sea floor, however, showed some surprises. Such mapping began in the 1930’s but accelerated during World War II with the advent of submarine warfare. Princeton Geosciences Professor Harry Hess played a pivotal role; as captain of the USS Cape Johnson he used the ship’s echo-sounder to “ping” the seafloor and measure depth as the ship traversed the Pacific Ocean between battles. After the war, this data led him to propose seafloor spreading, a process crucial to the development of the theory of plate tectonics. Modern methods to measure bathymetry include multi-beam echo sounders that map a wide swath of seafloor, and satellite measurement of variations in sea level due to variations in gravitational pull over bathymetric features – sea level is slightly lower over low spots on the sea floor and slightly higher over high spots. 4. Using Google Earth, “fly to” Challenger Deep, the deepest place on Earth (once Google Earth gets you there, you may have to zoom out to see where you are). Where is it? - Challenger deep is located in Mariana Trench in the Philippine Sea off the coast of Guam. 5. Challenger Deep reaches 11 km (36,000 ft) below sea level. Which is greater, the elevation of Mt Everest (see question 3) above sea level, or the depth of Challenger Deep below sea level, and by how much? - On Google Earth, Challenger Deep is approximately 10382 meters below sea level. This depth below sea level is greater than Mt. Everest’s elevation by 1626 meters.

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