Uranium series ages of the Del Mar Man and Sunnyvale skeletons

Bischoff and Rosenbauer claim that their uranium series ages for the Del Marman and Sunnyvale skeletons indicate that the previously published aspartic acid racemization ages of these two skeletons are too old. They state that the concordancy of their 230Th and 231Pa ages supports the uranium series ages for the bone samples. Uranium series ages, however, are based on the critical assumption that bones incorporate uranium for only a relatively short time after their burial and have subsequently remained closed systems with respect to migration of both uranium and its daughter isotopes 230Th and 231Pa. We maintain that the assumption of rapid uranium incorporation followed by closed system behavior is tenuous and that 230Th-231Pa concordancy is a necessary but not sufficient condition to establish this behavior and thus the accuracy of the dates