Stable Isotope Geochemistry

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ClaytonEAR-0126185Oxygen isotopic compositions of primitive Solar System materials have proved to be very powerful tracers of chemical process involved in formation of objects as small as chondrules to as large as planets. Isotopic compositions serve to determine genetic associations of divers meteoritic groups, such as the SNC (martian) meteorites and the HED (howardite, eucrite, diogenite) groups. Low-temperature aqueous processes in carbonaceous chondrites have been studied in terms of reservoir origins, alteration conditions and water/rock ratios. All this has been possible even though we lacked consensus on the ultimate origin of the "anomalous" effects. A novel approach, combining photochemistry and the X-wind model of stellar accretions, has the possibility of providing a consistent picture of oxygen isotopic evolution, along with a novel interpretation of the chemical evolution of the inner Solar System. In addition, we plan to use oxygen isotopic compositions of organic molecules in carbonaceous meteorites to determine how much of the organic chemistry occurred within the parent asteroid, and how much occurred earlier, in the Solar Nebula or in interstellar space. These are fundamental questions for the origin of pre-biotic organic molecules.