Optical configuration and the racemisation of amino acids in sediments and in fossils — A review

Abstract

The optical configuration of amino acids in sediments and fossils has been reviewed and the results have been used to evaluate critically the reputed occurrence of original amino acids in ancient sediments of the Mesozoic, Palaeozoic and Precambrian eras. A racemic mixture of amino-acid enantiomers and diastereoisomers in the Messel Oil Shale of the Eocene Epoch has been reported and the results used to interpret the presence of contaminant amino acids in bone samples from hominid cave sites at Sterkfontein and Makapansgat, South Africa. The racemisation reaction of amino acids in sediments and fossils has been discussed and the validity of using kinetic data as a geochronologic method has been questioned. The degree of racemisation of aspartic acid, alanine, valine and leucine in Egyptian mummy tendon has been studied. Kinetic data, obtained from experiments carried out at elevated temperature, have been used to calculate an average in situ reaction temperature for this sample. Data whose interpretation questions the reliability of amino-acid dating and palaeotemperature calculations have been presented.