AstroMeso

According to Milankovitch (1941) theory, 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 other planets. These variations can be traced over several millions of years (Ma) in the geological sedimentary records, although the mechanisms that transfer the forcing insolation to the sedimentary variations are not precisely known. After the pioneer work of Hays et al (1976), a large effort of the stratigraphic community has been devoted to the search of this astronomical imprint. Over the last three decades, the Earth’s orbital and spin solutions elaborated by the PI and his group (Laskar et al, 1993, 2004, 2011a) have been used in a collaborative effort that allowed to establish for the Neogene (0-23Ma) a geological timescale based on the astronomical solution (Lourens et al, 2004; Hilgen et al, 2012). Nevertheless, extending this procedure through the Mesozoic Era (66-252 Ma) 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, 2011b). For three decades, the astronomical orbital solutions elaborated by the PI have been used by geologists to establish local or global time scales. This project is specifically designed to achieve the opposite. We will use the geological record as an input to break the horizon of predictability of 60Ma which results from the chaotic nature of the orbital 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 the Mesozoic Era. This will open a new era where the geological record will actually be used to retrieve the orbital evolution of the solar system. 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 (http://www.cnrs.fr/en/when-geology-reveals-solar-systems-past-secrets). At the same time, numerous studies appear involving very long sedimentary records (Ma et al, 2017, 2019). The objectives that many have dreamed for twenty years are thus now at hand. AstroMeso aims to go one step beyond by gathering a unique team with world leaders in celestial mechanics and planetary motions and world leaders in cyclostratigraphic analysis of long sedimentary records. AstroMeso will support two postdocs. One in astronomy for the search of an optimal orbital and insolation solution, and the other in geology, who will collect and analyse the best records. Both will work in close connection with the teams of the project, maintaining a strong interaction between astronomy and geology all along the duration of the project. This interdisciplinary, necessarily interdisciplinary, project, between geology and astronomy, searching to retrace the history of the Earth and the solar system trough the geological record, fits perfectly with the INSU-CNRS will to develop transversality around fundamental questions.