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Our transcription: The central idea of plate tectonics is simple. The Earth's crust and upper mantle are broken into about a dozen large rigid plates, somewhat like segments of cracked shell on a hardboiled egg. These gigantic slabs of rock slip and slide as they are carried about by the convection currents in the partially molten layer of the upper mantle. A similar pattern of crustal plate motion is sometimes observed on the surface of molten lava lakes. The cooled skin of lava across the lake is broken into plates by the turbulent liquid beneath.
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