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# Plate Tectonics: Floating Crustal Sections (page 2)

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Author: Janice VanCleave

1. According to the theory of plate tectonics, the Earth's lithosphere is divided into sections called plates. These plates float on top of the asthenosphere much like flat rocks on thick mud. Use an earth science text to find out about the lithospheric plates. Prepare a display diagram showing the shapes, names, and locations of the plates. For information about plate tectonics, see Thomas R. Watters, Planets (New York: Macmillan, 1995), pp. 84–85.
2.

1. The boundary where lithospheric plates move away from each other, such as at the midocean ridges, is called a divergent boundary. Prepare a model of plates at a divergent boundary: Cover a small box with a solid-color paper and label it "Asthenosphere." Lay two sponges on top of the box so they are slightly separated. Label each sponge "Plate" and add directional arrows, indicating movement of the plates in opposite horizontal directions. Make a stand-up sign by folding an index card in half lengthwise and labeling the card "Divergent Boundary."
2. Use the previous method to prepare models for a transform boundary (a place where two plates slide horizontally in opposite directions alongside each other) and a convergent boundary (a place where two plates collide and usually one plate moves under the other). For more information about the differences between these three boundaries, see Keith Stowe, Essentials of Ocean Science (New York: Wiley, 1987), pp. 26–35. Make a model showing the boundaries at which crustal material is created, destroyed, and neither created nor destroyed.

### Get the Facts

1. Alfred Wegener (1880–1930), a German scientist, was the first to propose the theory known as continental drift. Find out about Wegener's theory. How is it alike or different from the theory of plate tectonics? What was Pangaea? For information about continental drift, see Janice VanCleave's Oceans for Every Kid (New York: Wiley, 1996), pp. 5–11.
2. In 1960, Harry Hess (1906–1969), an American geologist, proposed the theory of seafloor spreading. Find out about the events that led Hess to his conclusion that the seafloor is spreading. For information about Hess, see John S. Dickey, Jr., On the Rocks (New York: Wiley, 1988), pp. 145–148.
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