Carbon compounds in terrestrial samples and the Orgueil meteorite

Meteorites contain extraterrestrial carbonaceous materials. The Alais, Orgueil, Tonk, and Ivuna meteorites resemble in their carbon, free sulfur, and non-metamorphosed mineral contents, densities, and general appearances certain organic-rich terrestrial sediments. Structural and isotopic determinations of carbon compounds in the Orgueil chondrite indicate that these compounds are primarily indigenous. Benzene extractable carbonaceous materials from Orgueil fragments and terrestrial sediments have similar chromatographic properties. Infrared and ultraviolet spectra show that they contain compounds of the same functional types. Mass spectrometric analyses of the alkanes from the Orgueil meteorite, sediments and organisms are statistically indistinguishable at the 95 per cent confidence level. Theoretical considerations and experimental data are presented which support the view that alkanes are well constituted to serve as indicators of former life. Complex alkanes in living things are structurally and isotopically analogous to hydrocarbons in petroleum. Pristane and phytane are constituents of a crude oil that is more than a billion years old. The structures and abundances of many alkanes in various sedimentary environments attest to the source and stability of these compounds. Based on the characteristics and distributions of organic substances on Earth, alkanes may provide the clearest insight into the origin of some carbonaceous substances in chondrites.