Astronomical Solutions over Geological Time

ongoing

According to Milankovitch (1941), some of the large climatic changes of the past originate in the variations of the Earth’s orbit and of its spin axis resulting from the gravitational pull of the planets and the Moon. These variations can be traced over several millions of years (Ma) in the geological sedimentary records. Over the last three decades, the Earth’s orbital and spin solutions elaborated by the PI and his group (Laskar et al, 1993, 2004, 2011) have been used to establish a geological timescale based on the astronomical solution (e.g. Lourens et al, 2004; Hilgen et al, 2012). Nevertheless, extending this procedure through the Mesozoic Era (66-252 Ma) and beyond is difficult, as the solar system motion is chaotic (Laskar, 1989, 1990). It will thus not be possible to retrieve the precise orbital motion of the planets beyond 60 Ma from their present state (Laskar et al, 2011). The PI's astronomical solutions have been used by geologists to establish local or global time scales. AstroGeo is designed to achieve the opposite. We will use the geological record as an input to break the horizon of predictability of 60Ma resulting from the chaotic motion of the planets. This will be done in a quantitative manner, and aims to provide a template orbital solution for the Earth that could be used for paleoclimate studies over any geological time. This project stems from the achievement of Olsen et al (2019) where for the first time, in a study that involves the PI, it was possible to precisely recover the frequencies of the precessing motion of the inner planets. AstroGeo will not provide a single or a few solutions, but a whole database of solutions that would equally fit all available astronomical observations. This will open a new era where the geological records will be used to retrieve the orbital evolution of the solar system. It will thus open a new observational window for retrieving not only the history of the Earth, but of the entire solar system.