Earth’s oxygen-rich atmosphere will be depleted in one billion years, study says

TOKYO, Japan — The oxygen-rich atmosphere which makes Earth habitable continues to exist thanks to the photosynthetic organisms which span the entirety of planet’s surface. However, due to the steady decrease of CO₂ in the atmosphere and global warming, a recent study finds these organisms that make up Earth’s biosphere may not be able to keep the planet alive in the distant future.

In a recent study, researchers used a model which measures biogeochemical processes on Earth and mimics Earth’s climate. The team used a statistical approach to account for the uncertainties in the evolution of Earth’s atmosphere. The assessment predicts that the oxygen-rich atmosphere will disappear within one billion years. Knowledge of this timescale could mean a different outcome for the planet or a push to find other habitable planets outside of Earth’s solar system.

“For many years, the lifespan of Earth’s biosphere has been discussed based on scientific knowledge about the steadily brightening of the sun and 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,” says Kazumi Ozaki, assistant professor at Toho University, in a media release.

Oxygen only has a ‘short’ window in Earth’s existence?

Christopher Reinhard, associate professor at Georgia Institute of Technology worked with Ozaki to create and test the model. Researchers tested their model over 400,000 times, changing a model parameter after each try. The results reveal that oxygen levels will be depleted in approximately one billion years, creating a vastly different, uninhabitable planet.

Ozaki and Reinhard referred to the Great Oxidation Event that occurred on Earth about 2.5 billion years ago. Prior to the event, Earth was only able to sustain organisms capable of surviving without oxygen.

“The atmosphere after the great deoxygenation is characterized by elevated methane levels, low-levels of CO₂, and no ozone layer. The Earth system will probably be a world of anaerobic life forms,” Ozaki adds.

Oxygen is necessary for the maintenance of all life forms as well as the production of the ozone layer, which protects the Earth’s surface from harmful radiation. However, according to this study, oxygen levels may only persist for about 30 percent of Earth’s existence as a habitable planet. The most distinct biosignature of life is oxygen which is what scientists look for in the search for other habitable planets. However, scientists must also consider other biosignatures that apply to poorly oxygenated planets as well as planets without oxygen when searching for other habitable planets.

The findings appear in the journal Nature Geoscience.

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