U-series Dating and Human Evolution

Abstract

Some of the major events in human evolution occurred during the Middle Pleistocene. These include the evolutionary rise of the Neanderthals in Eurasia and of anatomically modern humans either in Africa or on a broader geographical front, in addition to major biogeographic changes among mammals including the hominine colonization of Europe. Prior to the Middle Pleistocene, the application of Potassium-Argon and Argon-Argon dating has yielded a relatively detailed chronological picture for the earlier phases of hominid evolution, and from c. 50 ky radiocarbon dating provides the backbone of our chronology for the extinction of the Neanderthals, colonization of Europe by anatomically modern humans and all subsequent events. Between these, however, the Middle Pleistocene has only been amenable to precise chronometric dating for the past few decades. Before the advent of radiometric dating, as Glynn Isaac (1975) famously observed, the Middle Pleistocene was “the muddle in the middle.” U-series dating is one of a range of dating methods employed by archaeologists to provide a chronology for human evolution (Fig. 1⇓). Other applicable methods include optically stimulated luminescence (OSL), which can be used to date sediments perhaps back to about 0.5 My, measuring the time since the last exposure to sunlight. It is increasingly employed as a dating method especially since suitable sediments are common on archaeological sites (e.g., Aitken 1992). A related technique, Thermoluminescence (TL), can be used to date burnt flint artifacts (e.g., Aitken 1985), which provide a more direct date for specific human activity on a site, although material that is suitably burnt is relatively rare. Potassium-Argon and Argon-Argon dating have been the most useful techniques for calibrating early hominid evolution because its limit for dating extends considerably beyond the origins of the earliest hominids at around 5 My (e.g., Curtis and Hay 1972). Their application, however, is …