AsianScientist (Mar. 2, 2021) – In around one billion years, our planet’s oxygen-rich atmosphere will return to the oxygen-poor, methane-rich composition reminiscent of early Earth. This finding, published in Nature Geoscience, hints that atmospheric oxygen is impermanent on habitable worlds—potentially affecting the search of life on other Earth-like planets.
Before it was eclipsed by Avengers: Endgame, the science-fiction epic Avatar was the highest-grossing film worldwide for nearly a decade. While close encounters with blue-skinned humanoids are still out of reach, scientists continue to search for signs of life across the universe.
One indicator that a planet may support life is the presence of oxygen in the atmosphere. After all, on Earth, organisms like plants, algae and cyanobacteria convert sunlight and carbon dioxide into oxygen. However, just how long the air we breathe will last in the Earth’s atmosphere remains uncertain, especially in the distant future.
To clear the air surrounding the fate of Earth’s oxygen, Professor Kazumi Ozaki from Toho University and Associate Professor Christopher Reinhard from the Georgia Institute of Technology modelled the planet’s climate, biological and geological processes to estimate the timescale of the Earth’s atmospheric conditions.
They found that Earth’s current atmosphere will likely persist for another one billion years before the Sun’s increasing brightness triggers the rapid loss of oxygen. As the Sun grows hotter, carbon dioxide in the atmosphere will absorb more heat and break down. Eventually, levels of carbon dioxide will become so low that photosynthetic organisms will be unable to produce oxygen and go extinct.
This mass extinction event will then prompt oxygen levels to drop sharply to conditions similar to that of the early Earth before the Great Oxidation Event around 2.5 billion years ago. To compensate for the lack of oxygen, methane levels will increase to levels 10,000 times higher than the amount in our atmosphere today.
Their model also suggests that atmospheric oxygen on Earth may only be possible for up to 30 percent of a planet’s lifetime. If the same holds true for other planets, other signs of life should be considered in the continuous search for extraterrestrials.
“Our results have important implications for the search for life on Earth-like planets beyond our Solar System. From the perspective of planetary evolution, our results imply that atmospheric oxygenation is not a permanent condition on habitable worlds…and that only a fraction of Earth’s history will be characterized by robustly detectable oxygen,” concluded the authors.
The article can be found at: Ozaki et al. (2021) The future lifespan of Earth’s oxygenated atmosphere.
Source: Toho University; Photo: Unsplash.
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