Possible effects of diagenesis on the stable isotope composition of amino acids in carbonaceous meteorites

Abstract

The initial report of indigenous, non-racemic protein amino acids (L-enantiomer excess) in the Murchison meteorite was based on the fact that only eight of the twenty amino acids characteristic of all life on Earth was present in this stone 1 . The absence of the other protein amino acids indicated that contamination subsequent to impact was highly unlikely. The development of new techniques for determining the stable isotope composition of individual amino acid enantiomers in the Murchison meteorite further documented the extraterrestrial origins of these compounds 2,3 . The stable isotope approach continues to be used to document the occurrence of an extraterrestrial L-enantiomer excess of protein amino acids in other carbonaceous meteorites 4 . It has been suggested that this L-enantiomer excess may result from aqueous reprocessing on meteorite parent bodies 4,5 . Preliminary results of simulation experiments are presented that are used to determine the extent to which the stable isotope compositions of amino acid constituents of carbonaceous meteorites may have been altered by these types of diagenetic processes subsequent to synthesis.