Accelerator mass spectrometry radiocarbon ages of amino acid extracts from Californian palaeoindian skeletons

Abstract

A decade ago, aspartic acid racemization ages were determined for some skeletal remains found in California, near La Jolla, Del Mar and Sunnyvale, suggesting that people were present in North America during the Upper Pleistocene1,2. These ages were obtained from the aspartic acid racemization rate, which was calibrated using a radiocarbon date of 17,150 ± 1,470 yr BP determined for a skeleton found in Laguna Beach, California3,4. These studies generated an intense controversy not only about the antiquity of human beings in the New World5,6 but also about the validity of racemization-based ages6-9, and prompted efforts to date the finds by other means6,7,10,11. Here we have used accelerator mass spectrometry (AMS) to determine the radiocarbon ages of the amino acid extracts used in the original racemization studies. Our studies indicate that some of the controversial Californian skeletons, which had been assigned to the Upper Pleistocene, are in fact Holocene. Show more