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Plate Tectonics

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The theory that Earth’s lithosphere is broken into plates that move slowly over the asthenosphere.

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Lithosphere

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The rigid outer layer of Earth, made of the crust and the uppermost mantle.

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Asthenosphere

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The plastic-like layer below the lithosphere where rock flows under pressure.

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Pangaea

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The ancient supercontinent that included all of Earth’s landmasses.

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Mid-Ocean Ridge

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An underwater mountain chain where new ocean floor is formed through sea-floor spreading.

Front

Sea-Floor Spreading

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The process where magma rises from the mantle at mid-ocean ridges, creating new crust.

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Divergent Boundary

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A plate boundary where two plates move apart, creating features like mid-ocean ridges and rift valleys.

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Convergent Boundary

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A plate boundary where two plates move toward each other, forming mountains, trenches, or volcanic arcs.

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Transform Boundary

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A plate boundary where plates slide past each other, often causing earthquakes.

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Subduction Zone

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A region where one plate sinks beneath another into the mantle, destroying old crust.