The tidal rhythmites in the Proterozoic Big Cottonwood Formation (BCC) of Utah, the Neoproterozoic Elatina Formation of the Flinders Range of Southern Australia, and the lower Pennsylvania Mansfield Formation of Indiana indicate that the rate of retreat of the lunar orbit has been approximately constant since the late Precambrian and closely matches the present epoch value determined from Apollo lasers. Examination of a new (BCC) core leads to a slightly revised length of day (LOD) and modified values for other Earth-Moon dynamical parameters, thus implying the length of day 900 million years ago, reported earlier by Sonett et al. [1996> should be modified to ~18.9 hrs. ¿ 1998 American Geophysical Union