Transcription: The Earth's continents and oceans rest upon a layer of rock called the lithosphere. The lithosphere consists of roughly a dozen separate rock masses or plates. Plate tectonics is the theory that describes the motion of these plates. Beneath the lithosphere is the asthenosphere, a plastic layer of material that flows very slowly as it is heated from the mantle below. Some regions in the Earth's mantle are hotter than others. Above the hotter areas, material in the asthenosphere expands, becoming less dense than surrounding regions. It rises. Upon reaching the top of the asthenosphere, the mater ...
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