The Future Lifespan Of Earth's Oxygenated Atmosphere

Schematic model structure. Boxes denote reservoirs, whereas arrows denote flux terms. The model tracks the major reservoirs and transfer fluxes within the surface carbon (C), sulphur (S), oxygen (O), and phosphorus (P) cycles, along with a comprehensive treatment of ocean biogeochemistry, and long-term transfers between the crust-ocean-atmosphere system and the mantle. DOA = degree of anoxia.

Earth's modern atmosphere is highly oxygenated and is a remotely detectable signal of its surface biosphere. However, the lifespan of oxygen-based biosignatures in Earth's atmosphere remains uncertain, particularly for the distant future.

Here we use a combined biogeochemistry and climate model to examine the likely timescale of oxygen-rich atmospheric conditions on Earth. Using a stochastic approach, we find that the mean future lifespan of Earth's atmosphere with oxygen levels more than 1% of the present atmospheric level is 1.08+-0.14 billion years.

The model projects that a deoxygenation of the atmosphere, with atmospheric oxygen dropping sharply to levels reminiscnet of the Archaean Earth, will most probably be triggered before the inception of moist greenhouse conditions in Earth's climate system and before the extensive loss of surface water from the atmosphere. We find that future deoxygenation is an inevitable consequence of increasing solar fluxes, whereas its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean-atmosphere-crust system.

Our results suggest that the planetary carbonate-silicate cycle will tend to lead to terminally CO2-limited biospheres and rapid atmospheric deoxygenation, emphasizing the need for robust atmospheric biosignatures applicable to weakly oxygenated and anoxic exoplanet atmospheres and highlighting the potential importance of atmospheric organic haze during the terminal stages of planetary habitability.

K. Ozaki, C. Reinhard
Comments: Manuscript currently in press in Nature Geoscience
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (
DOI: 10.1038/s41561-021-00693-5
Cite as: arXiv:2103.02694 [astro-ph.EP] (or arXiv:2103.02694v1 [astro-ph.EP] for this version)
Submission history
From: Christopher Reinhard
[v1] Wed, 3 Mar 2021 21:26:46 UTC (2,428 KB)

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