The search for extraterrestrial life should not disregard planets with zero oxygen, as these other worlds may just be teeming with microbial life.
A team of researchers has found huge fluctuations in oxygen levels of ancient Earth that took place before the Great Oxidation Event.
They believe the same fluctuations could be happening in other planets, which means it is possible that planets with undetectable oxygen could be home to simple microorganisms that dominated the Earth a few billion years ago.
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