Organic Compounds in Meteorites

. There is little doubt that the bulk of the organic matter in meteorites is indigenous, judging from isotopic measurements on C, H, and S (20, 21). Such proof is not available for individual compounds, however, and it is therefore necessary to resort to less direct arguments to rule out terrestrial contamination. We shall briefly review the most reliably established features of organic matter in meteorites, and see. how well FTT reactions can account for them. Owing to space limitations, we can only give a concise summary of the most pertinent data. The interested reader may wish to consult the original sources, as well as the reviews of Hayes (22), Vdovykin (23). and Or6 and co’-workers (24). compounds were not confirmed at higher resolution (28), however, but can, in any event, be made in the FTT synthesis. The authors have found large amounts of cycloalkanes in a commercial Fischer-Tropsch sample. Carbon isotope fractionations. Meteorites show a very large-difference in *XC/lZC ratio between carbonate and organic carbon: 60 to 80 per mil (20, 21, 32). This trend remained unexplained for a number of years, because coexisting carbonate and organic matter on the earth shows a much smaller difference, typically 25 to 30 proposed that the two types of carbon came from two unrelated reservoirs while Arrhenius and Alfven (33) suggested fractionation during carbonate growth from the gas phase, involving multiple desorption or metastable molecules. It turns out, however, that the Fischer-Tropsch reaction gives an isotopic fractionation of just the right sign and magnitude, owing to a kinetic isotopic effect (34, 35). From the temperature dependence of the fractionation between 375’ and 550°K, the observed fractionations in Cl and C2 chondrites