Abstract
We have carried out AMS radiocarbon analysis on two groups of samples: the first one gave reasonable ESR age estimates and the second one yielded serious age underestinations. All samples were supposedly older than 35 ka, the oldest being around 160 ka. Two pretreatment techniques were used for radiocarbon dating: acid evolution and thermal release. Heating to 600, 750 and 900°C combined with total de-gassing at these temperatures was chosen to obtain age estimates on the organic fraction, secondary carbonates and original carbonate present in the hydroxyapatite mineral phase, respectively. All radiocarbon results present serious age underestimations. The secondary carbonate fraction gives almost modern results indicating an extremely rapid exchange of this component. Owing to this very rapid carbonate exchange it is not likely that the ESR signals used for dating are associated with the secondary carbonates. One tooth from Tabun with independent age estimates of >150 ka was further investigated by the Oxford AMS laboratory, yielding an age estimate of 1930±100 BP on the residual collagen from dentine and 18,000±160 BP on the carbonate component of the enamel bioapatite. We did not, however, find an explanation of why some samples give serious ESR underestimatioils whilst many others provide reasonable results.
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