GEOCHEMISTRY

scientific discipline that deals with the relative abundance, distribution, and migration of the Earth's chemical elements and their isotopes. Until the early 1940s geochemistry was primarily concerned with defining elemental abundances in minerals and rocks. Since that time, investigators have broadened the scope of their research significantly, studying, for example, the continual recycling of the Earth's constituent materials through agencies of the hydrosphere and atmosphere coupled with seafloor spreading, mountain building, and other processes involving the terrestrial crust. Modern geochemical research also includes the study of chemical transformations of biological materials in rocks and the cyclic flow of individual elements (and their compounds) between living and nonliving systems. Since the 1960s, certain areas of geochemical research have become interlinked with cosmologye.g., the study of the origin and relative abundance of elements in the solar system, the Milky Way Galaxy, and the universe as a whole; the chemical composition of meteorites; and the ages of terrestrial and lunar rocks.