The future lifespan of Earth's oxygenated Atmosphere

TL;DR

This study models Earth's future atmospheric oxygen levels, estimating a lifespan of about 1.08 billion years for oxygen-rich conditions, and predicts eventual deoxygenation driven by solar flux increases and planetary cycles.

Contribution

It introduces a combined biogeochemistry and climate model to project Earth's atmospheric oxygen lifespan and deoxygenation timeline under future solar and planetary conditions.

Findings

Future oxygen-rich atmosphere lasts approximately 1.08 billion years.

Deoxygenation likely occurs before moist greenhouse conditions.

Atmospheric deoxygenation is driven by increasing solar flux and planetary cycles.

Abstract

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.