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Inner Core

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The innermost and densest geological layer of the Earth. It is primarily a solid alloy of iron and nickel. It is at ~5,200°C and under 3.6 million atmospheres of pressure.

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Outer Core

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The layer of fluid iron-nickel alloy between the Earth's inner core and mantle. It is about 2,200 km thick and has a temperature between ~4,500 and 5,500°C.

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Mantle

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The semi-solid layer between the Earth's core and crust. It is 2,900 km thick. Convection currents in this layer allow the movement of tectonic plates in the crust.

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Crust

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The thinnest and outermost layer of the Earth. This layer is also the least dense. On Earth, there are two types, Continental and Oceanic.

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Oceanic Crust

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The thinnest and densest portion of the Earth's crust formed at the bottom of the ocean.

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Continental Crust

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The less dense portion of the crust that forms the land masses on Earth.

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Plate Tectonics

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The theory that explains how major landforms are created as a result of convection currents in the mantle.

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Continental Drift

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This theory preceded the modern theory of plate tectonics.

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Mantle Convection

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The slow movement of the semi-solid mantle as heat rises from the core to the surface and cooler material sinks. This movement drives the motion of tectonic plates.

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Convergent Boundary

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Any area of the planet where two or more tectonic plates collide. These boundaries experience compressive forces.