Recent studies suggest that Earth’s current oxygen-rich atmosphere, which has been a stable condition for millions of years, is not a permanent state. Instead, it is predicted to transition back to a methane-dominated atmosphere similar to its composition billions of years ago. While this atmospheric shift is not expected for another billion years, scientists anticipate a rapid and significant transformation once it commences.
LIFE BEYOND EARTH
Published in Nature Geoscience, the research also underscores the implications for the search for extraterrestrial life. Oxygen, previously considered a reliable biosignature for habitable exoplanets, may not be a consistent indicator. The Earth’s impending atmospheric transition serves as a cautionary note that the presence of oxygen alone should not be the sole criterion for identifying signs of life beyond our planet.
Using detailed models of Earth’s biosphere, scientists factored in changes in solar brightness and subsequent decreases in carbon dioxide levels. As carbon dioxide diminishes, photosynthesizing organisms like plants would produce less oxygen. Simulations indicated that the depletion of oxygen would precede the loss of oceans due to increased solar radiation, contrary to earlier predictions.
Earth scientist Chris Reinhard from the Georgia Institute of Technology explained, “The drop in oxygen is very, very extreme. We’re talking around a million times less oxygen than there is today.”
Beyond influencing our understanding of Earth’s future, this research has implications for the search for habitable exoplanets. As telescopes become more powerful, aiding in this exploration, it becomes crucial to broaden our understanding of potential biosignatures beyond oxygen. Initiatives like NASA’s NExSS project, focused on investigating the habitability of planets beyond our solar system, aim to provide valuable insights for these efforts.
According to calculations by Reinhard and environmental scientist Kazumi Ozaki from Toho University, Earth’s oxygen-rich phase is expected to last only 20-30 percent of its total lifespan. However, microbial life may persist in a methane-dominated atmosphere long after oxygen-dependent life forms cease to exist.
“The Earth system will probably be a world of anaerobic life forms,” stated Ozaki.
This glimpse into the future of our planet underscores the dynamic nature of habitability and emphasizes the importance of exploring diverse biosignatures in our ongoing quest for life elsewhere in the Universe.