Scientists predict that Earth’s oxygen-rich atmosphere will revert to a methane-rich, low-oxygen state in about a billion years, according to a 2021 study. This shift, reminiscent of pre-Great Oxidation Event conditions, will occur rapidly, making oxygen a temporary feature of habitable worlds. The findings suggest that the search for extraterrestrial life should consider other biosignatures besides oxygen. The research is part of NASA’s NExSS project, investigating planetary habitability.
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