An Etymological Dictionary of Astronomy and Astrophysics
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The rocky outermost layer of the Earth, ranging from about 10 to 65 km in thickness. It is distinguished from the underlying the → Earth's mantle layer by its more → silicon- and → aluminium-rich composition, lower density, and the lower velocity at which it conducts seismic energy. It includes → continental crust (about 40 km thick) and → oceanic crust (about 7 km thick). The crust and the topmost layer of the mantle form the → lithosphere. The five most abundant → chemical elements in the Earth's crust are, in percentage by weight of the Earth's crust: → oxygen (O) 46%, silicon (Si) 28%, aluminium (Al) 8%, → iron (Fe) 5%, and → calcium (Ca) 4%.

→ Earth; → crust.