Calculation of amino acid racemization ages based on apparent parabolic kinetics

Abstract

Amino acid racemization and epimerization reactions in carbonate fossils are non-linear and follow reversible first-order kinetics only to a d l -amino acid value of about 0.3 to 0.5. Although relative age relationships are not affected by non-linearity of the reaction rate, deviation from reversible first-order kinetics prevents simple linear extrapolation of the kinetic expression in order to estimate ages of fossils with high ratios. Instead of applying reversible first-order kinetics, the racemization and epimerization reactions can be modeled in terms of apparent parabolic kinetics, a procedure that generates a linear relationship between square root of age of samples and d l values. Data from a variety of speciments show that the relationship between square root of age and d l -amino acid is linear to a d l value of about 1.0. This approach provides a simple expression for calculating ages of fossils over a greater portion of the racemization and epimerization reaction range.