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10 February 2004 Amino acids in carbonaceous meteorites: biotic or abiotic?
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Carbonaceous meteorites are relics of ancient parent bodies from the time of formation of our solar system, about 4.5 billion years ago. They contain many of the organic compounds (e.g. amino acids) that are considered the building blocks of life. Experiments that attempt to simulate the synthesis of amino acids from inorganic precursors results in racemates. However, we have observed that several of the common protein amino acids in carbonaceous meteorites are non-racemeic, exhibiting an L-enantiomer excess typical of life. Stable isotope analysis of the individual amino acid enantiomers confirms that this L-excess is extraterrestrial, rather than contamination subsequent to impact. It has generally been assumed that these amino acids were formed by abiotic processes and were initially racemic, with subsequent partial destruction of their respective D-enantiomers by abiotic processes. However, the alternative scenario, i.e. the L-excess being a relic of ancient life, is largely ignored. Here we address this possibility based on the distributions, stereochemistry and stable carbon and nitrogen isotope compositions of the amino acids in carbonaceous meteorites.
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Michael H. Engel, Vlad E. Andrus, and Stephen A. Macko "Amino acids in carbonaceous meteorites: biotic or abiotic?", Proc. SPIE 5163, Instruments, Methods, and Missions for Astrobiology VII, (10 February 2004);

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