New insights in non-destructive direct dating of human remains

19th December 2012

Renaud Joannes-Boyau

To better understand human evolution, archaeologists require precise chronologies so as to compare and contrast fossil collections. While indirect dating of the sedimentary matrices of human occupation sites are considered somehow more precise than direct dating techniques, their accuracy is frequently poor.

Direct dating of human remains older than 40 to 50 ka is limited to U-series and electron spin resonance (ESR) techniques. To minimise the impact of direct dating on valuable and oftentimes fragile archaeological samples, new methods of non-destructive U-Th and ESR analyses were investigated, using specifically designed protocols. Both methods were seriously compromised by the fact that teeth accumulate large amounts of uranium following their deposition in sediments. In this research, we have used a laser ablation ICPMS mapping protocol to investigate the isotope distributions and elemental concentrations of uranium and thorium in fossil teeth. Enamel and dentine isotopic maps show complex patterns that imply that systematic mapping of  fragments  would  provide  accurate  insights  necessary for U-series and ESR internal dose assessments. A fossil Neanderthal tooth from Payre (France) showed negligible U-migration through the external enamel surface compared to the internal migration from the dentine, a result with substantive implications for ESR dating.

Non-destructive ESR analyses were carried out on enamel fragments rather than powder (the typical method) in efforts to  minimise  the  impact  of  analysis  on  samples.  Results reveal that the ESR spectra of enamel fragments have a high angular dependency, which complicates their study and the establishment  of  experimental  protocols. In  this  research, novel measuring protocols and analytical decomposition of ESR spectra have provided new insights into the composite nature of the signal. The development of a comprehensive model describing the influence of several oriented and non- oriented CO – radicals in the spectra with complex kinetics and transfer processes has shown that frequent underestimation can be expected for most fossil tooth enamel ages. The new model suggests that fossils such as the Kabwe Skull (Broken Hill,  Kabwe,  Zambia)  have  a  dose  underestimation  of approximately 30%. This study provides, for the first time, a precise, accurate and comprehensive model for virtually non- destructive direct dating of fossil remains using a combination of two key geochronological techniques, ESR and U-series.

Renaud Joannes-Boyau
New insights in non-destructive direct dating of human remains
2012
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Thesis Abstracts
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