Earth Will Lose Its Oxygen: Scientists Warn Of A Rapid Countdown

A recent study reveals that Earth's oxygen-rich atmosphere, vital for complex life, is expected to last approximately one billion more years. Increasing solar radiation will reduce atmospheric carbon dioxide, impairing photosynthesis and leading to a sharp decline in oxygen levels.

The study that was published in Nature Geoscience said that this deoxygenation could occur rapidly, rendering Earth inhospitable to most life forms. The findings also suggest oxygen may not be a permanent biosignature on habitable planets, impacting the search for extraterrestrial life.

"For many years, the lifespan of Earth's biosphere has been discussed based on scientific knowledge about the steady brightening of the sun and the global carbonate-silicate geochemical cycle. One of the corollaries of such a theoretical framework is a continuous decline in atmospheric CO2 levels and global warming on geological timescales. Indeed, it is generally thought that Earth's biosphere will come to an end in the next 2 billion years due to the combination of overheating and CO2 scarcity for photosynthesis. If true, one can expect that atmospheric O2 levels will also eventually decrease in the distant future. However, it remains unclear exactly when and how this will occur," environmental scientist Kazumi Ozaki from Toho University in Japan said when the study was published.

To examine how Earth's atmosphere will evolve in the future, Ozaki and Christopher Reinhard, Associate Professor at Georgia Institute of Technology, constructed an Earth system model which simulates climate and biogeochemical processes. Because modelling future Earth evolution intrinsically has uncertainties in geological and biological evolutions, a stochastic approach was adopted, enabling the researchers to obtain a probabilistic assessment of the lifespan of an oxygenated atmosphere. Ozaki ran the model more than 400 thousand times, varying the model parameters, and 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 atmosphere after the great deoxygenation is characterised by elevated methane, low levels of CO2, and no ozone layer. The Earth system will probably be a world of anaerobic life forms," says Ozaki.

Earth's oxygen-rich atmosphere represents an important sign of life that can be remotely detected. However, this study suggests that Earth's oxygenated atmosphere would not be a permanent feature and that the oxygen-rich atmosphere might only be possible for 20-30% of the Earth's entire history as an inhabited planet. Oxygen (and photochemical byproduct, ozone) is the most accepted biosignature for the search for life on exoplanets, but if we can generalise this insight to Earth-like planets, then scientists need to consider additional biosignatures applicable to weakly oxygenated and anoxic worlds in the search for life beyond our solar system.