For now, life is thriving on our oxygen-rich planet, but Earth hasn’t always been like this, and scientists have predicted that the atmosphere will return to a methane-rich, oxygen-poor state in the future.
It probably won’t happen for another billion years or so. But when changes come, it will happen pretty quickly.
This shift will return the planet to the state it was in before the so-called Great Oxidation (GOE) about 2.4 billion years ago.
Moreover, researchers believe that atmospheric oxygen is unlikely to be the main sign of habitability of planets, which is important for us in the search for signs of life in the universe.
“The model predicts that atmospheric deoxygenation, in which atmospheric O2 plummets to levels reminiscent of Archean Earth, is likely to occur before the onset of humid greenhouse conditions in the Earth’s climate system and before extensive loss of surface water from the atmosphere,” the researchers explained.
This will be the end for humans and most other life forms that rely on oxygen to get through the day, so let’s hope we figure out how to leave the planet at some point within the next billion years.
To arrive at their conclusions, the researchers developed 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 as heat levels rise. 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 the face of the Earth in about 2 billion years, but the model presented here, based on an average of just under 400,000 simulations, says that oxygen depletion would wipe out life first.
“The drop in oxygen is very, very extreme,” scientist Chris Reinhard of the Georgia Institute of Technology told New Scientist. “About a million times less oxygen than today.”
This study indicates the relevance of the search for habitable planets outside the solar system.
More and more powerful telescopes have been emerging recently , and scientists want to be able to know what they should be looking for in the arrays of data received by telescopes.
We may need to look for biosignals other than oxygen to have the best chance of detecting 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 the University of Toho in Japan, Earth’s oxygen-rich history will last only about 30 percent of the life of the planet as a whole, and microbial life will continue long after we are gone.
“The atmosphere after the great deoxygenation is characterized by high methane, low CO2 and no ozone layer,” Ozaki said. “The Earth System is likely to become a world of anaerobic life forms.”
An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenated environment.
The 3 anaerobes commonly isolated are Fusobacterium, Prevotella, and Bacteroides. In such an environment, intelligent life that has switched to digital format, or robots, could also survive.
The study is published in the journal Nature Geoscience.