Radiocarbon dating of biological apatites: A review
Abstract Since the early trials in the 50's, the reliability of 14C dates obtained from bioapatites has always been questioned. However, methodological attempts at dating biological apatites are rare. The compilation of the radiocarbon dates published in Radiocarbon over the period 1959–2009 shows that less than 6% of all the bone dates were performed on purified bioapatite. Crucial for the validation of the approach, is the design of tests for the preservation of the geochemical signal in biological apatites that are relevant for 14C dating. Because carbonate in apatite can exchange isotopically with dissolved carbon present in the environmental fluids, pretreatments are necessary but not sufficient and preservation criteria based on mineral integrity are of limited help. In this case, only an indirect approach, based on the dating of different bone/tooth fractions of the same individual and/or associated material is able to distinguish between preserved and altered fossils. In case of alteration, it is unlikely that the rate of isotopic exchange/recrystallization will be identical in skeletal tissues with different physico-chemical properties and any intra-individual difference measured in 14C age must result from differential diagenesis. We applied this strategy to more than 100 Holocene and Late Pleistocene localities worldwide. This approach confirms that carbonate in calcined bone is very resistant to post-burial isotopic exchange and is the most reliable source of inorganic carbon for 14C dating regardless of the environmental conditions. Large intra-individual differences in 14C age are found in several European and American localities, showing that both bone and enamel apatite can suffer from rejuvenation due to isotopic exchange during fossilization. On the contrary, the absence of significant intra-individual differences in 14C age in most of the localities from arid environments (Africa, Arabic Peninsula) attests to the good preservation of bone apatite in these regions. This contrasting situation confirms that bone diagenesis must be treated on a site-by-site basis, and demonstrates that bioapatite is a reliable material to date skeletal remains in arid environments.