In sediments spanning the last 9000 years from Saanich Inlet L enantiomers of amino acids are most abundant, but the percentages of D enantiomers increase with age, apparently because of partial racemization. Of the amino acids measured, glutamic acid and alanine show the greatest degree of racemization; leucine, isoleucine, and valine show the least.
Kvenvolden, Keith A., Etta Peterson and Frederick S. Brown. 1970. "Racemization of Amino Acids in Sediments from Saanich Inlet, British Columbia." Science 169 (3950): 1079-1082.