Earth's precession rate evolution and rapid fall during the Late Proterozoic

Abstract

We consider the use of cyclostratigraphic estimates of ancient Earth-axis precession rates, k, as a proxy for ancient length of day and ancient Earth-Moon distance. Analysis of published estimates for k indicate a statistically robust acceleration in the rate at which k fell during the Late Proterozoic. We investigate whether this accelerated fall-rate can be reasonably explained by an increase in tidal drag, at that time, or whether alternate explanations are needed. A tidal drag explanation requires an unusually large and long-lived resonance in Earth's oceans. However, alternate explanations are even less viable. A rearrangement of Earth's internal structure can be ruled out by the excessive geothermal heat production this would have caused, whilst mass redistribution due to Late Proterozoic glaciation can also be ruled out as the k-history did not return to its former trend after glaciation ended. Disruption of the Earth-Moon-Sun system by a nearby passing star is similarly unable to account for the observations since the required disruption is much too large to have happened without additional, clearly observable effects. We also consider a possible impact from thermally driven, atmospheric tides but reject this explanation as it would decelerate the fall in precession rather than accelerate it. These conclusions required development of novel techniques for inverse modelling the k-history to directly give (i) tidal-drag and (ii) the potential energy liberated by internal mass distribution.