Link established with emerging microbial activity on the primitive Earth

Scientists from PSL University, within the ENS – PSL and Paris Observatory – PSL, in collaboration with CNRS researchers members of the UMI iGLOBES of the University of Arizona, establish a link between the emerging microbial activity on the primitive Earth and the Earth’s climate, ice cycles and thus the habitability of our planet more than 3.5 billion years ago. Published in the journal Nature, on 1er June 2020, this work opens new perspectives to study the conditions of habitability elsewhere in the Universe.

In favour of the interdisciplinarity which the University PSL is committed to, and which is reflected in the creation in 2015 of the interdisciplinary research project “Origins and conditions of the appearance of life” (OCAV), researchers from the Paris Observatory – PSL, from the ENS – PSL within the Institute of Biology and from the CNRS within the UMI iGLOBES at the university of Arizona, have pooled their own expertise and simulation methods relating to planetary modelling on the one hand and ecological systems on the other.

This highly interdisciplinary work, identified since the beginning of the OCAV project as a unique contribution of PSL on this theme, consisted in coupling these two approaches to obtain the coupled evolution of atmospheric composition, climate, and biological activity. The first methane consuming and producing ecosystems, supposed to have appeared on Earth before photosynthesis more than 3.5 billion years ago, represent the elementary system for validating the relevance of this new approach to quantify the mutual impact of biological activity on climate and atmospheric composition.

This study shows that between 3.5 and 4 billion years before our era, the evolution of primitive ecosystems based on the production and consumption of methane, an atmospheric gas with a strong greenhouse effect, influenced, in connection with the carbon cycle, the terrestrial climate, the glacial cycles and thus the habitability of our planet. Biological activity thus exerted strong control over the atmosphere and climate very early in the history of our planet, several hundred million years before the appearance of the first oxygenated photosynthetic organisms led to the emergence of oxygen as a major gas in our atmosphere.

This general approach is now being applied to quantify the possibility of methanogenic activity at the heart of Enceladus, a moon of Saturn for which the Cassini probe measured the composition of the jets ejected at the surface, and on Mars, whose deep ground may have been habitable and inhabited throughout the last 4 billion years. The atmospheric biosignature of these ecosystems being very specific to them, this study suggests that the detection of methanogenic activity could be envisaged beyond our solar system, for Earth-like exoplanets that would offer conditions similar to those of the primitive Earth.


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