ESR dating studies of the australopithecine site of Sterkfontein, South Africa

We have used the ESR (electron spin resonance) method to determine the age of bovid tooth enamel from Member 4 of the Sterkfontein site. This member has previously yielded many skeletal remains of the species Australopithecus africanus. Alpha-spectrometric U-series analyses of one of the teeth suggests that U was continuously absorbed by the teeth during their burial history. Making the assumption of linear U uptake, we obtain an average age for Member 4 of 2·1 ± 0·5 Ma. The age distribution appears to be bimodal, however, with a major peak at 2·37 ± 0·29 Ma and a lesser peak at 1·72 ± 0·31 Ma. The lower age peak may represent admixture of teeth from a younger layer, probably Member 5. The ages are consistent with estimates based on faunal evolution. These data suggest that ESR dating of tooth enamel can be applied to sites with ages > 2 Ma, as long as the radiation dose rate is sufficiently low.