Declining oxygen will eventually suffocate most lives on Earth

For now, life thrives on our oxygen-rich planet, but Earth hasn’t always been so – and scientists have predicted that in the future the atmosphere will once again be rich in methane and poor in methane. oxygen.

It probably won’t happen for about a billion years. But when the change does happen, it will happen fairly quickly, suggests the study earlier this year.

This change will return the planet to something like the state it was in before what is known as the Great Oxidation Event (GOE) about 2.4 billion years ago.

Additionally, the researchers behind the new study say that atmospheric oxygen is unlikely to be a permanent feature of habitable worlds in general, which has implications for our efforts to detect signs of more life. far in the Universe.

“The model predicts that deoxygenation of the atmosphere, with a sudden drop in atmospheric O2 to levels reminiscent of Archean Earth, will most likely be triggered before the onset of humid greenhouse conditions in the Earth’s climate system. and before the significant loss of surface water from the atmosphere, ”the researchers wrote in their published article.

At this point, that will be the end of the road for humans and most other life forms that depend on oxygen to get through the day, so hopefully we can find a way out of the planet at some point in the years. 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 the corresponding drop in carbon dioxide levels, as the gas breaks down due to l ‘increased heat levels. Less carbon dioxide means less photosynthetic organisms such as plants, which would result in less oxygen.

Scientists have previously predicted that an increase in solar radiation would wipe ocean waters from our planet’s surface within about 2 billion years, but the new model – based on an average of just under 400,000 simulations – said that reducing oxygen will kill off life first.

“The drop in oxygen is very, very extreme,” said Earth scientist Chris Reinhard of the Georgia Institute of Technology. New Scientist earlier this year. “We’re talking about a million times less oxygen than there is today.”

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

More and more powerful telescopes are coming online and scientists want to know what to look for in the reams of data these instruments collect.

We may need to look for other biosignatures besides oxygen to have the best chance of spotting life, the researchers say. Their study is part of the NASA NExSS (Nexus for Exoplanet System Science) project, which studies the habitability of planets other than our own.

According to calculations made by Reinhard and environmental scientist Kazumi Ozaki of the University of Toho in Japan, the habitable history of the oxygen-rich Earth may only last 20-30% of the planet’s lifespan in its together – and microbial life will carry to exist long after we are gone.

“The atmosphere after the great deoxygenation is characterized by high methane, low CO2 levels and no ozone layer,” Ozaki said. “The Earth system is likely to be a world of anaerobic life forms.”

The research was published in Geosciences of nature.

A version of this article was first published in March 2021.

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