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Crust (geology)

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In geology, a crust is the outer layer of a planet, part of its lithosphere. Planetary crusts are generally composed of a less dense material than that of its deeper layers.

On partially-molten planets, such as Earth, the lithosphere is floating on fluid interior layers. Because of the partially-fluid upper mantle, or asthenosphere, underneath, floating lithospheres are often broken into tectonic plates that move. On Earth there are two types of crust: continental crust (sial) and the more dense oceanic crust (sima).

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Last updated: 02-10-2005 22:55:15
Last updated: 03-15-2005 09:25:26