Natural variations in the abundances of isotopes of the light elements oxygen, carbon and nitrogen will be used to study a variety of geochemical and cosmochemical problems. The fundamental thermodynamic basis of isotopic fractionation will be expanded by additional laboratory experiments and theoretical calculations. These results will be applied to the determination of thermal histories of igneous and metamorphic rocks. Particular emphasis will be given to rocks from the Earth's mantle in order to assess the degree of recycling of crustal rocks into the interior. The origin of the Earth and the nature of its raw materials will be studied through oxygen isotope abundances in meteorites. The three-isotope method is a very powerful tool for establishing genetic relationships among the various constituents of the early Solar System. Meteorite studies will focus on the primitive carbonaceous chondrites, in particular, on the processes of hydration and dehydration in asteroidal bodies. Some carbonaceous chondrites contain abundant organic compounds, including amino acids and carboxylic acids, which may have been formed either in the nebula or within asteroidal parent bodies. The site of formation of these compounds will be determined by measurements of their oxygen isotopic compositions.
