The Future of Earth: Oxygen Levels Predicted to Plummet in a Billion Years
Complex life on Earth thrives today due to its abundant oxygen supply, but this may not be the case forever. Scientists predict that in the distant future, our planet’s atmosphere will transition back to a state rich in methane and low in oxygen, resembling conditions before the Great Oxidation Event 2.4 billion years ago.
While this dramatic shift is not expected to occur for another billion years, research published in 2021 suggests that when it does happen, it will happen rapidly. Environmental scientist Kazumi Ozaki from Toho University in Japan explained, “For many years, the lifespan of Earth’s biosphere has been discussed based on scientific knowledge about the steadily brightening of the sun and global carbonate-silicate geochemical cycle.”
The study indicates that atmospheric oxygen is unlikely to be a permanent feature of habitable worlds, posing challenges for detecting life beyond our planet.
The researchers project a drastic drop in atmospheric oxygen levels, leading to a world reminiscent of the Archaean Earth era. This shift could spell the end for oxygen-dependent life forms, including humans, within the next billion years.
To reach these conclusions, detailed models of Earth’s biosphere were run, considering changes in the Sun’s brightness and decreasing carbon dioxide levels due to increased heat.
Less carbon dioxide means fewer oxygen-producing organisms like plants, resulting in a decline in oxygen levels. The research suggests that oxygen depletion may precede the loss of ocean waters, indicating a grim fate for life on Earth.
As we search for habitable planets beyond our Solar System, this study underscores the importance of looking for alternative biosignatures apart from oxygen. The NASA NExSS project is exploring the habitability of exoplanets, shedding light on the potential diversity of life in the universe.
According to the researchers’ calculations, Earth’s oxygen-rich phase may only last 20-30% of its total lifespan, with microbial life persisting long after oxygen-dependent organisms perish.
“The atmosphere after the great deoxygenation is characterized by elevated methane, low levels of CO2, and no ozone layer,” Ozaki stated. “The Earth system will probably be a world of anaerobic life forms.”
This research was published in Nature Geoscience.
An earlier version of this article was published in March 2021.
