In earth science, the part of the Earth that starts about 1,800 mi (2,900 km) beneath the surface and extends downward. It consists largely of an iron-rich metallic alloy and is thought to have a two-part structure: an outer fluid region and a solid, extremely dense inner region that measures only about 1,500 mi (2,400 km) across. The alloy composition is mainly iron with small amounts of nickel. This composition is deduced from the chemistry of iron meteorites that presumably came from the breakup of a planetary body that also had an iron core. See also crust; mantle.

This entry comes from Encyclopædia Britannica Concise.
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