Plate Tectonics and Geological Concepts

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Plate tectonics

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The idea that Earth’s outer shell is made up of big pieces (plates) that slowly move over time.

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Tectonic plate

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Large, rigid pieces of Earth’s crust and upper mantle that fit together like puzzle pieces.

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Lithosphere

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The rigid outer layer of Earth, which includes the crust and top part of mantle, where the plates are.

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Asthenosphere

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The softer, partially melted layer beneath the lithosphere on which the plates move.

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Continental drift

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The old idea that continents slowly drift across Earth’s surface.

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Pangaea

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A supercontinent (all the land in one piece) that existed long ago, before the continents drifted apart.

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Seafloor spreading

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The process where new oceanic crust is made at mid-ocean ridges as plates move apart.

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Subduction

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When one tectonic plate moves under another and sinks into the Earth’s mantle.

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Geological time

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The very long timescales (thousands to millions of years) over which plate movements happen.

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Evidence for plate tectonics

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Clues like matching coastlines, fossils, rock layers, and magnetic stripes on ocean floors that show plates used to be together.