Origins of the L-amino acid excess in carbonaceous meteorites

Carbonaceous meteorites provide the best direct evidence for the types and abundances of organic compounds that were present at approximately the time of formation of our solar system. The occurrence of eight amino acids in carbonaceous meteorites that are ubiquitous to all life as we know it has led to much discussion concerning their significance for the origin of life. The fact that several of the protein amino acids in carbonaceous meteorites have been reported to contain an L-enantiomer excess led to the initial speculation that the preferred stereochemistry for the organic constituents of life as we know it was derived from this extraterrestrial source1. Hypotheses that have been used to explain this extraterrestrial L-amino acid excess are discussed within the context of the results of recent laboratory experiments.