Increasing accuracy for the radiocarbon dating of sites occupied by the first Americans

Genetic analysis of Paleoamerican human remains suggests that people first entered the Americas sometime between ∼14,000 and ∼16,000 years ago. Evaluation of these data requires unequivocal archaeological evidence in a solid geological context that is well dated. Accurately determining the age of late Pleistocene sites is thus crucial in explaining when and how humans colonized the Americas. There are, however, significant challenges to dating reliability, especially when vertebrate fossils (i.e. bones, teeth and ivory) are often the only datable materials preserved at sites. We re-dated vertebrate fossils associated with the North American butchering sites of Wally's Beach (Canada), La Prele [also known as Fetterman (Wyoming)], Lindsay (Montana), and Dent (Colorado). Our work illustrates the crucial importance of sample chemical preparation in completely removing contaminants derived from sediments or museum curation. Specifically, our work demonstrates that chromatographic methods, e.g. preparative High Performance Liquid Chromatography and column chromatography using XAD resins, are currently the only efficient methods for removing environmental and museum-derived contaminants. These advanced techniques yield demonstrably more accurate AMS 14C measurements that refine the ages of these four sites and thereby contribute to advancing our understanding of human dispersals across North America during the late Pleistocene