Geoscience: Earth’s atmosphere may return to low-levels of oxygen in one billion years

In approximately one billion years, Earth’s oxygen-rich atmosphere will return to an oxygen-poor, methane-rich composition, according to a paper published in Nature Geoscience. This finding suggests that atmospheric oxygen is not permanent on habitable worlds, which has implications for the search for life on other Earth-like planets.

An indicator of possible planetary life is a detectable, oxygen-rich atmosphere, which suggests the existence of plants and photosynthesis. Earth’s highly oxygenated present-day atmosphere is a hallmark of its biosphere. However, the lifespan of these oxygen-based biosignatures in Earth’s atmosphere is uncertain, particularly for the distant future.

Kazumi Ozaki and Christopher Reinhard modelled Earth’s systems, including climate and biological and geological processes to examine the timescale of the atmospheric conditions on Earth. They found that Earth’s oxygen-rich atmosphere will probably persist for another one billion years before rapid deoxygenation renders the atmosphere reminiscent of early Earth before the Great Oxidation Event around 2.5 billion years ago. The authors suggest that the detection of atmospheric oxygen on Earth might only be possible for 20–30% of the planet’s lifetime. If the same is true for other planets, the authors argue, then additional biosignatures are needed in the search for extraterrestrial life.