Dating of bones and teeth

EU and LU are not the only uptake models that have been proposed. More mathematically sophisticated models have been developed (e.g., Szabo and Rosholt 1969 Hille 1979 Chen and Yuan 1988), in some cases using both the U and U decay chains (see Ivanovich 1982 Millard and Pike 1999 for summaries). While there have been some apparently successful applications of these models, none have been found to be universally applicable, and the search for a reliable method of U-series dating of bones and teeth continues. In the last decade or so, two important new approaches to the modeling of U uptake in bones and in teeth have been developed. These are discussed in detail below. 

Chen T, Ynan S (1988) Uraninm-series dating of bones and teeth from Chinese Paleohthic sites. Archaeometry 30 59-76... 

In 1988, Chen and Yuan published U-series dates on bones and teeth for more than 20 Chinese sites, providing the first extensive Palaeolithic chronology for China. They used a-spectrometric measurements of °Th/U, and and used concordance... 

Archaeological fragments of bones and teeth take up fluorine from the surrounding soil and accumulate it in their mineral phase when they are exposed to a humid environment. Geological time spans are needed for this process to reach equilibrium and for the fluorine distribution to become uniform. In cortical parts of long bone diaphysis, an initially U-shaped fluorine concentration profile can be observed, which decreases from the outer surface and the marrow cavity towards the inner parts of the bone and carries information on the exposure duration of the buried object in its shape. The time dependence of the profile slope is usually described in a simplified way by a diffusion model. The quantitative mathematical evaluation of these profiles may provide information on the exposure duration and the physical condition of the samples. Therefore, several attempts to use fluorine profiling as a dating method have been undertaken [3,39], The distribution of... 

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. 

An alternative to the early uptake assumption, linear uptake, assumes that bones and teeth continue to take up Uranium at a constant rate (Ikeya 1982 Bischoff et al. 1995), giving a U-series date something over twice that calculated using the EU assumption. Although more common for teeth than for bone, both EU and LU dates are often quoted for the same sample, with the implication that the true age of the sample probably lies somewhere in between. 

There are a few developments on the horizon that will increase our ability to date bones and teeth reliability. Both y- and a-spectrometric methods can measure Pa/ U and °Th/U and concordance between dates calculated using the two can provide a measure of reliability. However, the discordance between the two is not very sensitive to different uptake regimes, and it is difficult to resolve, for example, bones that have undergone EU from those that have undergone LU with the analytical errors commonly encountered in measurements by y- and a-spectrometry. On the other hand, it has been shown recently that TIMS can measure both isotopic ratios with a precision usually better than 1% (Edwards et al. 1997). TIMS measurements of Pa/ U and °Th/U have yet to be routinely applied to dating fossil remains, but in the future, concordance between the two decay series will provide further evidence of the validity of a particular uptake model to a particular sample. 

A.A.-M. Gaschen, Relevance of fluorine diffusion for exposure age dating in archaeological bones and teeth, Unpublished PhD Thesis, University of Bern, 2005. 

Matter consists of atoms that are made up of protons (electropositive), electrons (electronegative), and neutrons (electrically neutral). Because the number of electrons and protons is equal, elements, atoms with different numbers of protons, have different numbers of electrons. The chemical properties of an element depend on the number of electrons, but because the electrons have almost no mass, the atomic weight of an element is its number of protons and neutrons. Neutrons are needed to hold the protons together in the nucleus. Isotopes are elements with different numbers of neutrons. Isotopes with too many neutrons are unstable and emit radioactivity. Radioactive and nonradioactive isotopes are used to follow biochemical reactions in health and disease, to date paleontology specimens, usually bones and teeth, and detect traces of life in ancient rocks. 

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... 

Bada, J.L., Paleoanthropological applications of amino acids racemization dating of fossil bones and teeth, Anthrop. Anz., 45, 1, 1987. 

Plenary 79. FI G M Edwards, e-mail address h.g.m.edwards bradford.ac.uk (NIR-FTRS). A review of recent applications of RS to archeology—characterizing ancient pigments, human skin, bone, ivories, teeth, resins, waxes and gums. Aging effects and dating possibilities. Emphasizes use of microscopic Raman. 

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