AstroGeo, winning project of ERC Advanced Grants Scholarships

On March 31, 2020, the European Research Council (ERC) awarded a researcher from the IMCCE one of its 185 grants intended to carry out daring and innovative projects, opening up new paths in their discipline or in other areas.

Link : https://erc.europa.eu/news/erc-2019-advanced-grants-results

The ERC Advanced Grants grants finance high-risk exploratory research projects of 5 years duration, with a maximum budget of 2.5 million euros each.

Led by Jacques Laskar, CNRS research director and director of the Institut de Mécanique Céleste et du calcul des éphémérides - IMCCE, within the Paris Observatory, AstroGeo is one of this year's selected projects.

AstroGeo project

According to Milankovitch's theory (Milankovitch, 1941), part of the great climatic changes of the past is due to the variations of the insolation on the surface of the Earth resulting from the deformation of its orbit resulting from the gravitational disturbances of the other planets. These variations can be found in the stratigraphic records accumulated over several million years (Ma). The correlation between the geological data and the calculations of celestial mechanics is sufficiently established so that since 2004, the geological time scales of the most recent periods are established from the astronomical solutions developed at IMCCE (Laskar et al, 2004) (http://vo.imcce.fr/insola/earth/online/earth/earth.html). Since then, a major effort has been devoted to extend this astronomical calibration over ever longer periods covering the entire Cenozoic, up to 66 Ma. In these works, the astronomical solution, given by calculation, is used to calibrate the geological data.

However, extending this work is difficult because celestial mechanics does not allow us to retrace the planetary orbits beyond 60 Ma due to the chaotic nature of the movement of the planets, highlighted by Jacques Laskar thirty years ago. The AstroGeo project aims to overcome this predictability horizon, imposed by the laws of gravitation by using ancient geological data as an additional constraint in obtaining astronomical solutions. In this ambitious project which makes it possible to reconstruct the orbits of the planets of the solar system, the limit is no longer imposed by the exponential propagation of uncertainties, with an almost impassable horizon at 60 Ma, but by the quality of the sedimentary data which could be used until very remote times, going as far as the Archean, 3 billion years ago.

The feasibility of the AstroGeo project was demonstrated with the publication in PNAS (Olsen et al, 2019) by an international team including Jacques Laskar, of a study showing how the analysis of sediment data from the Newark basin had made it possible to find the state of the solar system 200 Ma ago (https://www.imcce.fr/news/mouvements-planetaires-geologie).

AstroGeo will more generally benefit from the very numerous collaborations established for three decades by Jacques Laskar with geologists around the world, with in particular in France, the ISTEP laboratory (Institute of Earth Sciences in Paris, UMR 7193), partner of IMCCE as part of the National Agency for Research AstroMeso project started in October 2019. AstroMeso is part of the wider AstroGeo project, and allowed to recruit a post-doctoral researcher to study sediment data from the Paris basin and the Vocontian basin in the South-East of France (Fig. 1).

Fig1
Fig1. These sedimentary alternations of layers of marl and limestone from South-East France date from around 130 Ma. They are attributed to the precession cycles of the Earth's spin axis with a period of around 20 ka and their amplitudes are modulated by variations in the eccentricity of the Earth, with periods of 100 ka and 405 ka due to the gravitational disturbances of other planets (1 ka = 1000 years).

Since the first long-term solution of the movement of the planets established by Urbain Le Verrier in 1840, and used by Milutin Milankovitch a century later to establish the astronomical theory of climates, the Paris Observatory has provided most of the planetary solutions which were used to correlate changes in insolation on the Earth's surface with glacial or sedimentary records. AstroGeo aims to continue this tradition of excellence by transforming the way solutions will be distributed to the paleoclimate community. Instead of producing a single reference solution which serves as the basis for establishing the geological time scale, which is no longer possible beyond 60 Ma, AstroGeo will provide a set of solutions, all compatible with the best observations from the moment, also giving users the possibility to search among these solutions, those which will best correspond to the newly collected data. The solution could then be constrained by these new stratigraphic data.

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