Cyclostratigraphy is severely compromised because many important Milankovitch cycles periods (e.g. obliquity) are directly affected by the poorly constrained Earth-Moon separation history. There is strong evidence that the Moon formed at 4.5 Ga just beyond the Roche limit (i.e. around 30 thousand km from Earth) and tidal drag has since pushed the Moon out to 384 thousand km today. But, for all intermediate times, neither theory nor observations provide strong constraints. Classic studies (e.g. Gerstenkorn, 1967) and more recent research (e.g. Green and Huber, 2014) strongly indicate that tidal drag varied dramatically through time but the detailed evolution is unknown. This project will provide tighter theoretical and observational constraints on past Earth-Moon separation by answering the overarching question: How has the lunar recession rate changed over geological time?
Our objectives are therefore:
- Improve understanding of the tidal evolution of the Earth-Moon system. We will use a two-pronged approach: (i) “turn cyclostratigraphy on its head” by using ancient Milankovitch cycles to constrain lunar distance; (ii) improve understanding of the controls on tidal-drag variation through Earth history by sensitivity analysis of a well-founded model of modern Earth tides. Improved understanding of evolution of the Earth-Moon system will enable the remaining objectives –
- Improve estimates of ancient Milankovitch cycle periods.
- Estimate the size of Milankovitch cycle uncertainties.
- Improve understanding of fluctuating insolation and changing tidal patterns in the deep past.