A chronometric investigation of the initial peopling of the Americas
Keywords: chronology
archaeological science
Bayesian modelling
North America
radiocarbon dating
archaeology

The initial peopling of the American continent marks a major event in the expansion of humans across the planet. For most of the 20th century, it was believed that a group of big-game hunters initially entered North America approximately 13,500 years ago, through the now flooded land bridge of Beringia, between modern day Siberia and Alaska. Once across, they would have moved southward through an ice-free corridor formed between the Laurentide and Cordilleran ice sheets, which began their recession after the last Ice Age. This model, however, was effectively refuted in 1997 when archaeologists found evidence in Chile, South America, which was reliably older than the North American record suggested. Today, questions associated with this dispersal are debated in First American research, and remain largely unanswered. These include the antiquity and origin of the initial arrivals, the number of migrational episodes, and the impact of human expansion in the late Quaternary faunal extinctions. In response, considering that timing is fundamental in the study of human dispersals, this investigation employs radiocarbon dating and Bayesian age modelling to build a robust chronological framework with which to elucidate broad spatio-temporal patterns. This is accomplished by obtaining reliable radiocarbon measurements for key archaeological sites across the continent, resolving dating discrepancies using a single-amino-acid isolation method, and building largescale Bayesian age models to track human presence and frame current evidence. This involved the laboratory processing of dateable material from 18 archaeological sites, the production of 133 radiocarbon dates, and the statistical analysis of archaeo-chronometric data from 41 archaeological sites in North America and Beringia. A widely used method, called ‘14C-dates-asdata’, is assessed from a radiocarbon dating perspective, and the potentially confounding effects introduced by challenges in sample processing in the analysis are demonstrated. This approach is the only other quantitative technique apart from Bayesian age modelling that uses the chronometric record to elucidate large-scale population events. Here, however, it is argued that Bayesian age modelling is the most efficient tool in tackling human dispersals.
Results obtained in this thesis have enabled the creation of a new Bayesian age model for the initial peopling of the Americas. This suggests that the earliest arrivals to mid-latitude North America were humans from eastern Asia, who most likely crossed near the end of the LGM. The synchronous commencement of Beringian, Clovis and Western Stemmed cultural traditions is also identified, and their overlap with the last appearance dates for 18 extinct genera suggests that human expansion was a key driver behind animal extinction events. Notably, these findings overturn the widespread notion that North America was first penetrated only after 16-15,000 years ago.
It is hoped that, in the future, new evidence in First Americans research will increase the resolution of the models here created, and enhance the conclusions drawn. Particular attention should be paid to Central and South America, regions with more limited archaeo-chronometric data and immediate chronometric potential. Improved chronological control in these regions is key in understanding the pattern of American settlement.