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For now, life is thriving on our oxygen-rich planet, but Earth hasn’t always been so – and scientists have predicted that in the future the atmosphere will revert to a methane-rich atmosphere and poor in oxygen.
It probably won’t happen for about a billion years. But when the change does happen, it will happen fairly quickly, the study suggests.
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 projects that deoxygenation of the atmosphere, with atmospheric O2 dropping sharply 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. surface water from the atmosphere, ”the researchers write 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 figure out how to leave the planet at some point in the next one. billion years. .
To draw 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, increasing levels of carbon dioxide. heat. Less carbon dioxide means less photosynthetic organisms such as plants, which would result in less oxygen.
Scientists previously predicted that increased 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 – says that reducing oxygen will kill life first.
“The drop in oxygen is very, very extreme,” said Earth scientist Chris Reinhard of the Georgia Institute of Technology. New scientist. “We are talking about a million times less oxygen than 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 be able to know what to look for in the reams of data these instruments collect.
We may have 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 by Reinhard and environmental scientist Kazumi Ozaki of the University of Toho in Japan, the oxygen-rich habitable history of the Earth could end up lasting only 20-30% of the planet’s lifespan. as a whole – and microbial life will bear 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,” explains Ozaki. “The earth system is likely to be a world of anaerobic life forms.”
The research was published in Geoscience of nature.
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