Enjoy while you can: Oxygen depletion will one day lead to the death of most living things on Earth

(ORDO NEWS) — For now, life thrives on our oxygen-rich planet, but Earth hasn’t always been like this – and scientists predict that in the future, the atmosphere will return to one rich in methane and low in oxygen.

It may not happen until a billion years from now. But when changes do come, they will come fairly quickly, according to a study published in 2021.

This shift will return the planet to a state similar to what it was in before the so-called Great Oxidizing Event (GOE) about 2.4 billion years ago.

What’s more, the authors of the study argue that atmospheric oxygen is unlikely to be a constant feature of habitable worlds in general, with implications for our efforts to detect signs of life further in the universe.

“The model predicts that atmospheric deoxygenation, with a sharp decrease in atmospheric O2 to levels reminiscent of Archean Earth, is likely to occur before the onset of wet greenhouse conditions in the Earth’s climate system and before extensive loss of surface water from the atmosphere,” the researchers explain in their paper.

At this point, it will be the end of the road for humans and most other life forms that depend on oxygen to get through the day, so let’s hope we figure out how to leave the planet within the next billion years.”

To reach their conclusions, the researchers ran detailed models of the Earth’s biosphere, taking into account changes in the Sun’s brightness and a corresponding drop in carbon dioxide levels as the gas is broken down by increasing amounts of heat. Less carbon dioxide means fewer photosynthetic organisms like plants, which will result in less oxygen.

Scientists previously predicted that increased radiation from the Sun would wipe out ocean waters from our planet in about 2 billion years, but this model – based on an average of just under 400,000 simulations – says that oxygen depletion would kill life first.

“The drop in oxygen is very, very extreme,” earth scientist Chris Reinhard of Georgia Tech told New Scientist. “We are talking about the fact that there will be a million times less oxygen than today.”

What makes the study especially relevant to today is our search for habitable planets outside the solar system.

Telescopes are getting more powerful, and scientists want to know what they should be looking for in the data sets these instruments are collecting.

It’s possible that in order to have the best chance of detecting life, we need to hunt for other biosignatures as well as oxygen, the researchers say. Their study is part of NASA‘s NExSS (Nexus for Exoplanet System Science) project, which studies the habitability of planets other than ours.

According to calculations by Reinhard and environmental scientist Kazumi Ozaki of the University of Toho in Japan, Earth’s oxygen-rich, habitable history may last only 20 to 30 percent of the planet’s total lifespan—and microbial life will persist long after our extinction.

“The atmosphere after the great deoxygenation is characterized by increased methane content, low CO2 levels and the absence of an ozone layer,” says Ozaki.

“The Earth system is likely to be a world of anaerobic life forms.”

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