Geochemistry is the study of the chemical and structural composition and evolution of Earth and its component parts, including the atmosphere, hydrosphere, crust, mantle, and core, as well as extraterrestrial matter, such as meteorites and comets, other planets, the sun, and distant stars. It concerns itself with the distribution and migration of elements within the Earth and its atmosphere. Over time, geochemistry has evolved from a descriptive science to one increasingly concerned with the mechanisms behind its observations. Geochemistry today is diversified into many subfields, including aqueous geochemistry, cosmochemistry, inorganic geochemistry, isotope geochemistry, organic geochemistry, and trace-element geochemistry. Since most geological processes involve chemical reactions, geochemistry and geochemical data are also used to explain many of these processes in other areas of the geosciences.

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