Amino acid racemization dating of fossil bones

Abstract

The development of amino acid racemization as a dating technique holds considerable promise for resolving questions of human evolution and culture histories. The advantages of this method are: fossil bone can be directly dated; only gram quantities are needed for analysis; and the range extends beyond that of radiocarbon. Amino acid racemization rates are dependent upon both time and temperature. In order to eliminate the need for evaluating the temperature history of a bone before it can be dated by racemization, a procedure has been developed wherein the in situ racemization rate is determined from the extent of racemization in a radiocarbon‐dated bone. Once this ‘calibration’ has been completed for a particular site, other bones from the area can be dated. Racemization ages deduced using this procedure are shown to be in close agreement with radiocarbon dates. The effects which other physical factors (pH, humidity, leaching) have on racemization rates are discussed. Because of the close correlation between temperatures calculated from in situ racemization rates (under diverse environmental conditions) and actual mean annual temperatures at various sites throughout the world, we conclude that factors other than temperature have very small effects on the reaction rate. The use of amino acid racemization in dating fossil man is illustrated by the racemization analyses of several North American paleo‐indian skeletons, the results of which provide additional evidence that man was present in North America more than 40,000 years ago.