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Earth-like planets orbiting M-dwarfs are prominent future targets whensearching for life outside the solar system. We apply our newly developedCoupled Atmosphere Biogeochemistry model to investigate the coupling betweenthe biosphere, geosphere and atmosphere to gain deeper insight into theatmospheric evolution of Earth-like planets orbiting M-dwarfs. Our main goal isto understand better atmospheric processes affecting biosignatures and climateon such worlds. Furthermore, this is the first study to our knowledge whichapplies an automated chemical pathway analysis quantifying the production anddestruction pathways of O$_2$ for an Earth-like planet with an Archean O$_2$abundance orbiting in the habitable zone of the M-dwarf AD Leo. Results suggestthat the main production arises in the upper atmosphere from CO$_2$ photolysisfollowed by catalytic HO$_x$ reactions. The strongest destruction does not takeplace in the troposphere, as was the case in Gebauer et al. (2017) for anearly-Earth analog planet around the Sun, but instead in the middle atmospherewhere H$_2$O photolysis is the strongest. This result was driven by the strongLyman-$\alpha$-radiation output of AD Leo, which efficiently photolyzes H$_2$O.Results further suggest that early Earth-like atmospheres of planets orbitingan M-dwarf like AD Leo are in absolute terms less destructive for atmosphericO$_2$ than for early-Earth analog planets around the Sun despite higherconcentrations of reduced gases such as e.g. H$_2$, CH$_4$ and CO. Hence thenet primary productivity (NPP) required to produce the same amount ofatmospheric O$_2$ at the surface is reduced. This implies that a possible GreatOxidation event, analogous to that on Earth, would have occurred earlier intime in analog atmospheres around M-dwarfs.

astrobiology

Evolution of Earth-like planetary atmospheres around M-dwarf stars:  Assessing the atmospheres and biospheres with a coupled atmosphere  biogeochemical model