For now, life is thriving on our oxygen-rich planet, but Earth wasn’t always like this – and scientists have predicted that in the future, the atmosphere will return to one that is rich in methane and low in oxygen.
This probably won’t happen for a billion years or so. But if the change comes, it will happen pretty soon, the study suggests.
This shift 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.
In addition, the researchers behind the new study say that oxygen from air is likely not a permanent feature of habitable worlds in general, affecting our efforts to detect signs of life further afield in the Universe.
The model projects that a deoxygenation of the atmosphere, in which atmospheric O2 falls sharply to levels reminiscent of the Archaic Earth, will most likely be activated before the onset of humid greenhouse conditions in the Earth’s climate system and before the extensive loss of surface water. atmosphere ‘, the researchers write in their published paper.
At that point, it’s 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 get off the planet sometime in the next billion years. come. .
To arrive at their conclusions, the researchers used 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 is broken down by increasing heat. Less carbon dioxide means less photosynthesizing organisms such as plants, which would result in less oxygen.
Scientists have previously predicted that more radiation from the sun would sweep ocean water off our planet’s surface in about 2 billion years, but the new model – based on an average of nearly 400,000 simulations – says the reduction in oxygen will be deadly. of 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 there is now.”
What makes the study particularly relevant to the present time 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 vast amounts of data these instruments collect.
We may need to hunt for other biosignatures in addition to 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 investigates the habitability of planets other than ours.
According to the calculations of Reinhard and environmental scientist Kazumi Ozaki, of Toho University in Japan, Earth’s oxygen-rich habitable history could ultimately last only 20-30 percent of the planet’s total lifespan – and will involve microbial life. on existing long after we are gone.
“The atmosphere after the great deoxygenation is characterized by increased methane content, low CO2 content and no ozone layer,” said Ozaki. “The Earth system will likely be a world of anaerobic life forms.”
The research is published in Nature Geoscience