Holocene age of the Yuha burial: direct radiocarbon determinations by accelerator mass spectrometry.

The view that human populations may not have arrived in the Western Hemisphere before about 12,000 radiocarbon yr BP has been challenged by claims of much greater antiquity for a small number of archaeological sites and human skeleton samples. One such site is the Homo sapiens sapiens cairn burial excavated in 1971 from the Yuha desert, Imperial County, California. Radiocarbon analysis of caliche coating one of the bones of the skeleton yielded a radiocarbon age of 21,500 +/- 1,000 yr BP, while radiocarbon and uranium series analyses of caliche coating a cairn boulder yielded ages of 22,125 +/- 400 and 19,000 +/- 3,000 yr BP, respectively. The late Pleistocene age assignment to the Yuha burial has been challenged by comparing the cultural context of the burial with other cairn burials in the same region, on the basis of the site's geomorphological context and from radiocarbon analyses of soil caliches. In rebuttal, arguments in defence of the original age assignment have been presented as well as an amino acid recemization analysis on the Yuha skeleton indicating an age of 23,600 +/- 2,600 yr BP. The tandem accelerator mass spectrometer at the University of Arizona has now been used to measure the ratio of 14C/13C in several organic and inorganic fractions of post-cranial bone from the Yuha H. sapiens sapiens skeleton. Isotope ratios from six chemical fractions all yielded radiocarbon ages for the skeleton of less than 4,000 yr BP. These results indicate that the Yuha skeleton is of Holocene age, in agreement with the cultural context of the burial, and in disagreement with the previously assigned Pleistocene age of 19,000-23,000 yr.

Middle holocene age of the sunnyvale human skeleton.

A morphologically modern human skeleton from Sunnyvale, California, previously dated by aspartic acid racemization to be approximately 70,000 years old and by uranium series isotopic ratios to be 8300 and 9000 years old, appears to be younger when dated by the carbon-14 method. Four carbon-14 determinations made by both decay and direct counting on three organic fractions of postcranial bone support a middle Holocene age assignment for the skeleton, probably in the range of 3500 to 5000 carbon-14 years before the present. This dating evidence is consistent with the geologic, archeological, and anthropometric relationships of the burial as well as previously determined carbon-14 determinations on associated materials.