For now, life is flourishing on our oxygen-rich planet, but Earth has not always been like that – and scientists have predicted that in the future, the atmosphere will return to a methane-rich and oxygen-poor one.
This will probably not happen for another billion years. But when the change comes, it will happen fairly quickly, the study suggests.
This change will take the planet back to something similar to the state it was in before what is known as the Great Oxidation Event (GOE) about 2.4 billion years ago.
Moreover, 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 further signs of life in the Universe.
“The model projects that a deoxygenation of the atmosphere, with atmospheric O2 falling sharply to levels reminiscent of Archaean Earth, will most likely be triggered before the start of wet greenhouse conditions in the Earth’s climate system and before the widespread loss of surface water from atmosphere “, the researchers write in their published paper.
At that time it will be the end of the road for human beings and most other life forms that rely on oxygen to get through the day, so hopefully figure out how to get off the planet at some point in the next billion years. years .
To reach their conclusions, the researchers made detailed models of the Earth’s biosphere, taking into account changes in the Sun’s brightness and the corresponding decrease in carbon dioxide levels, as the gas decomposes with increasing heat levels. Less carbon dioxide means fewer photosynthesizing organisms, such as plants, which would lead to less oxygen.
Scientists have previously predicted that increased radiation from the Sun will wipe the ocean’s waters off our planet in about 2 billion years, but the new model – based on an average of just under 400,000 simulations – says reducing oxygen will kill more first of life.
“The decrease in oxygen is very, very extreme,” said Chris Reinhard, an Earth scientist at the Georgia Institute of Technology. The new scientist. “We’re talking about a million times less oxygen than we have today.”
What makes the study particularly relevant to 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 they should look for in the data that these instruments collect.
We may need to look for biosignatures other than oxygen to have the best chance of observing life, the researchers say. Their study is part of NASA’s NExSS (Nexus for Exoplanet System Science) project, which investigates the habitability of planets other than our own.
According to calculations by Reinhard and environmental scientist Kazumi Ozaki of Toho University in Japan, the oxygen-rich habitable history of the Earth could last only 20-30 percent of the life of the planet as a whole – and microbial life will lead to existence long after I’m gone.
“The atmosphere after the great deoxygenation is characterized by high methane, low CO2 levels and no ozone layer,” says Ozaki. “The Earth system will probably be a world with anaerobic life forms.”
The research was published in Geoscience of nature.