Missing Obliquity Signal in Late Paleocene and Early Eocene Climate Records due to Solar System Chaos

The dynamical evolution of the solar system is chaotic with a Lyapunov time of only ~5 Myr for the inner planets. Due to the chaos it is fundamentally impossible to accurately predict the solar system's orbital evolution beyond ~50 Myr based on present astronomical observations. We recently developed a method to overcome the problem by using the geologic record to constrain astronomical solutions in the past. Our resulting optimal astronomical solution (called ZB18a) shows exceptional agreement with geologic records to ~58 Ma (Myr ago) and a characteristic resonance transition around 50~Ma. Here we show that ZB18a and integration of Earth's and Mars' spin vector based on ZB18a yield reduced variations in Earth's and Mars' orbital inclination and Earth's obliquity (axial tilt) from ~58 to ~48 Ma. The changes in the obliquities have important implications for the climate histories of Earth and Mars. For instance, reduced variations in Earth's obliquity from ~58 to ~48 Ma would have affected Earth's climate across the late Paleocene - early Eocene (LPEE). Remarkably, a nearly ubiquitous phenomenon in long-term geologic records across the LPEE is a very weak or absent obliquity signal. We propose here that the reduced amplitude in Earth's obliquity, as predicted by our astronomical solution ZB18a, contributed to the weak/absent obliquity signal in geologic records from ~58 to ~48 Ma. Dynamical chaos in the solar system hence not only affects its orbital properties, but also the long-term evolution of planetary climate through eccentricity and the link between inclination and axial tilt.