Application and Ar-Ar Calibration of Uranium-Series Dating at Olorgesailie

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With support from the National Science Foundation, Drs. Kenneth Ludwig, Alan Deino, and Warren Sharp will collect and analyze samples for Argon-Argon dating, and analyze existing samples for uranium-series dating, from the classic Olorgesailie archeological area in southern Kenya. Olorgesailie, with its extremely rich accumulation of early human artefacts and continuous record of human occupation, has been studied for over 50 years, most recently by the ongoing studies or Richard Potts and colleagues at the Smithsonian Institution. The pre-600,000 year record at Olorgesailie is now well-dated, as the result of previous Argon-Argon dating by Deino. However, the younger part of the record, which contains one of the very few records of the transition from Acheulean technology (a relatively crude stone industry characteristic of relatively small-brained Homo Erectus) to Middle Stone Age technology (related to anatomically near-modern humans) of is only now being studied in detail. Few dates of any kind are available for this part of the Olorgesailie stratigraphy, however, and none of high precision. It is just this gap which we will fill with the research of this proposal, in part by applying a relatively new but well-validated and extremely high-precision method - uranium-series by thermal ionization mass spectrometry - to new types of samples that have been shown to be common at Olorgesailie. These new types of samples - of which the most promising is root-casts which have been replaced by the opal form of silica - have not been used before for Uranium-series dating, so their reliability and accuracy are unvalidated. Fortunately (and very unusually), such validation can be carried out at Olorgesailie because of the common co-occurrence of samples for uranium-series dating with samples of volcanic ash for Argon-Argon dating, the latter being the acknowledged "gold standard" for archaeological dating in the time-range of 50,000 years to millions of years. If validated, the uranium-series dates can then be used to provide age control on those parts of the younger Olorgesailie beds that lack ash beds suitable for Argon-Argon dating. With the anticipated age control provided by this research, the detailed studies by Smithsonian Institute scientists (who recently obtained a 5-year National Science Foundation grant to continue their research at Olorgesailie) on the evolution of human culture and behavior in East Africa will gain an invaluable and precise dimension of age control at a level that is unprecedented in a single-site study of long-term human evolution over the past 500,000 years. This project will thus by highly synergistic with other federally-funded research (especially given the significant degree of cost sharing of this project), as well as providing valuable experience to a work-study student in applied high-technology methods in archeology and geology.