Outermost solid part of the Earth, essentially composed of a range of igneous and metamorphic rock types. In continental regions, the crust is made up chiefly of granitic rock, whereas the composition of the ocean floor corresponds mainly to that of basalt and gabbro. On average, the crust extends 22 mi (35 km) downward from the surface to the underlying mantle, from which it is separated by the Mohorovicic discontinuity (the Moho). The crust and top layer of the mantle together form the lithosphere.
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