Plate Tectonics

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Plate tectonics is a relatively new theory that has revolutionized the way geologists think about the Earth. According to the theory, the surface of the Earth is broken into large plates. The size and position of these plates change over time. The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building. Plate tectonics is a combination of two earlier ideas, continental drift and sea-floor spreading. Continental drift is the movement of continents over the Earth's surface and in their change in position relative to each other. Sea-floor spreading is the creation of new oceanic crust at mid-ocean ridges and movement of the crust away from the mid-ocean ridges.

The lesson starts with a description of the chemical and physical layers of the Earth. Then the historical development of the plate tectonic theory is described. The lesson concludes with descriptions of the location and types of plate boundaries. This lesson is longer than most . A concise classroom presentation might describe the layers of the Earth, location of plate boundaries, and types of plate motion.

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