A team led by Jacques Laskar from the Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE) and the Paris Observatory has released new computational results for the long-term evolution of the orbital and rotational motion of the Earth. Following Milankovitch’s theory of the paleoclimate that describes how major climatic changes on Earth are affected by astronomical events, these results have been employed to provide a new calibration of the sedimentary records over the 0 – 23.03 Myr geological period (the so-called Neogen period). Thus, Laskar et al.’s work has contributed to the definition of the new Geological Time Scale that has been adopted by the International Commission of Stratigraphy (ICS) and the International Union of Geological Sciences (IUGS). It is the first time that astronomical computations have been used to establish the ICS geological chronology over a full geological period.
Due to gravitational planetary perturbations, the orbit of the Earth slowly changes over time, as does the orientation of the planet’s spin axis. These changes induce variations of the solar radiation received on the Earth’s surface that are responsible for some of the large climatic changes of the past. The major effects of astronomical phenomena on the Earth’s climate were first described by the Serbian mathematician Milankovitch in his theory of the paleoclimate (1941). In 1976, Milankovitch’s theory was validated in the landmark work of Hays, Imbrie and Shackleton, who measured the change in continental ice volume over time through the variation of the isotopic ratio of oxygen in marine sediments. The succession of the Ice Ages that occurred during the Pleistocene epoch (between 10 000 yrs and 1.8 million yrs (Myr) ago) has been shown to be related to the periodic changes of the Earth’s orbit and rotational parameters. Since then, the Milankovitch theory has been confirmed: the variation of the Earth’s orbital parameters regulates some of the major changes in the Earth’s climate.
Therefore, the computation of the evolving planetary orbits is of major interest to those who try to understand the past and future of the Earth’s climate. Such computations, provided by astronomers, were used by Milankovitch to establish his theory. Indeed, he used the orbital computations made in 1856 by Le Verrier, former director of the Paris Observatory and famed discoverer of Neptune in 1846. Since then, the Paris Observatory’s teams have continued to be involved in the computation of the variations of planetary orbits over an extended time span. In addition to providing tools for the understanding of the Earth’s major climatic changes, computations of planetary orbits make it possible to refine the geological time scale used by geologists. A fundamental step to understanding the Earth’s past chronology is the establishment of a complete, precise time scale for geological records. The Geologic Time Scale depends on two aspects of the dating of the records. First, the sedimentary records that are collected worldwide must be linked together through significant events, such as the appearance/disappearance of living species or the paleomagnetic reversals. The sedimentary records can then be associated to a relative timescale.
Jennifer Martin | alfa
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