NOAA/WDS Paleoclimatology - Atlantic and Pacific Foraminiferal Amino Acid Racemization Data

Isoleucine, one of several amino acids isolated from a suite of
well-dated deep-sea cores, shows a progressive increase in the
degree of racemization with the age of the sediment. Amino acids
in sediments show an initial rate of racemization almost an order
of magnitude faster than the rate observed for free amino acids
at a comparable pH and temperature. The observed kinetics depend
on a variety of diagenetic processes, but it appears that the
ratio of alloisoleucine to isoleucine is a reliable indicator
of age for samples less than 400,000 years old; for older samples
the results are more ambiguous. Isoleucine is racemic in samples
older than about 15 million years.