Description du projet
Le champ magnétique terrestre et la disparition des Néandertaliens
Le champ magnétique de la Terre a diminué d’environ 20 % au cours des 150 dernières années. La Terre étant constamment soumise au rayonnement cosmique, l’intensité de celui‑ci dépend de la force du champ magnétique. À l’échelle des temps géologiques, il y a eu des périodes d’effondrement du moment dipolaire magnétique, et donc du champ magnétique, qui peuvent être associées à des changements de polarité du dipôle ou à de simples excursions géomagnétiques (EG). Durant ces périodes, le rayonnement UV pénètre plus profondément dans l’atmosphère. Le projet REVA, financé par l’UE, étudiera cette fenêtre UV pendant les événements EG de Laschamps-Mono Lake. Ceci est important compte tenu de sa globalité et des implications possibles pour l’évolution humaine (contemporaine de la disparition des Néandertaliens).
Objectif
"The Earth is constantly subjected to cosmic radiation, the intensity of which, at the level of the upper atmosphere and the Earth's surface, depends on the strength of the magnetic field (MF) surrounding our planet. Over geological timescales, there have been periods of collapse of the magnetic dipole moment, and therefore of the MF, which can be associated with changes in the polarity of the dipole or with simple geomagnetic excursions (GE). GE events (typically lasting ~1ka to ~10ka) generate an increase in cosmic bombardment in the upper atmosphere and, ultimately, through chemical effects the destruction/thinning of the ozone layer. During these periods UV radiation can penetrate deeper into the atmosphere, while it is otherwise absorbed by the ozone layer. Yet, the reality of such a UV ""window” has never been attested by natural observations, which if present during GE events in the future would have significant environmental and above all human consequences. This is plausibly foreseen in a short term as the intensity of Earth’s MF has decreased (~20%) over the past 150 years and with an accelerated rate in the last decades (> ~10 times the normal). The aim of this project is, therefore, to test the reality of a UV window during the Mono Lake-Laschamps (~ -40 ka) GE event, which by its magnitude, its globality and the possible implications for human evolution (being contemporaneous with the disappearance of the Neanderthals), is an example of a remarkable case study. Here, by measuring stable isotopic composition of sulfur (S) at high resolution (<200 years) in ice cores taken in Antarctica, we will leverage peculiar aspects of atmospheric chemistry of the S-33 isotope. In the absence of ozone, the interaction between SO2 and UV radiation, through photochemical processes, generates mass-independent (Δ) signatures. We propose to trace a possible UV ""window"" by analyzing the evolution of the observed ΔS-33 anomaly and model the extent of depletion of ozone layer."
Champ scientifique
Mots‑clés
Programme(s)
Régime de financement
MSCA-IF - Marie Skłodowska-Curie Individual Fellowships (IF)Coordinateur
75794 Paris
France