M. J. M. Turnbull & S. Moorbath comment: The paper of Yang et al. (1996) describes a novel dating approach, using the Sm–Nd method on phosphatic material, to determine the age of the Precambrian–Cambrian boundary. The dates reported are of a precision which, in light of the relatively small range of 147Sm/144 Nd ratios (0.09–0.17), is surprising. We have recalculated the published data using the ISOPLOT program of Ludwig (1991) and this is shown below in Table 1. These results cast considerable doubt on the statistical analysis of Yang et al. (1996). While this technique may have utility with Precambrian successions it would appear to be of limited use for the high precision dating required for Phanerozoic stratigraphic correlation.