Bone, archaeological uranium-series dating

The co-occurrence of archaeological deposits with datable calcite is unfortunately rare, and because of this, attempts have been made to date more controversial materials (e.g., bones and teeth). Bones and teeth present particular problems for uranium-series dating because they remain open systems. Uranium is taken up from the burial environment, and can also be lost, and a model of this migration is required to calculate a date from the measured isotope ratios. One approach utilizes a model of the diffusion of uranium into a bone that predicts specific distributions of uranium and uranium-series isotopes across... 

Bones and teeth, however, are primary archaeological materials and are common to many archaeological sites. Bones bearing cut marks from stone tools are a clear proxy for human occupation of a site, and in the study of human evolution, hominid remains provide the primary archive material. Hence, many attempts have been made to directly date bones and teeth using the U-series method. Unlike calcite, however, bones and teeth are open systems. Living bone, for example, contains a few parts per billion (ppb) of Uranium, but archaeological bone may contain 1-100 parts per million (ppm) of Uranium, taken up from the burial environment. Implicit in the calculation of a date from °Th/U or Pa/ U is a model for this Uranium uptake, and the reliability of a U-series date is dependent on the validity of this uptake model. 

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