LATE PROTEROZOIC AND PALEOZOIC TIDES, RETREAT OF THE MOON, AND ROTATION OF THE EARTH

The tidal rhythmites in the Proterozoic Big Cottonwood Formation (Utah , United States), the Neoproterozoic Elatina Formation of the Flinders Range (southern Australia), and the Lower Pennsylvanian Pottsville Fo rmation (Alabama, United Slates) and Mansfield Formation (Indiana, Uni ted States) indicate that the rate of retreat of the lunar orbit is d xi/dt similar to k(2) sin(2 delta) (where xi is the Earth-moon radius vector, k(2) is the tidal Love number, and delta is the tidal lag angl e) and that this rate has been approximately constant since the late P recambrian. When the contribution to tidal friction from the sun is ta ken into account, these data imply that the length of the terrestrial day 900 million years ago was similar to 18 hours.