by R.F. Service, Feb 25, 2021 in ScienceAAAS

The first organisms to “breathe” oxygen—or at least use it—appeared 3.1 billion years ago, according to a new genetic analysis of dozens of families of microbes. The find is surprising because the Great Oxidation Event, which filled Earth’s atmosphere with the precious gas, didn’t occur until some 500 million years later.

“I was pretty thrilled to see this paper,” says Patrick Shih, an evolutionary biologist at the University of California (UC), Davis. The advent of proteins that can use oxygen, Shih and others say, marks a key step in the emergence of aerobic microbes, which are those able to harness oxygen. “The transition from a world that was mostly anaerobic to one that was mostly aerobic was one of the major innovations in life,” says Tim Lyons, a biogeochemist at UC Riverside.

Scientists broadly agree that Earth’s early atmosphere and oceans were all but devoid of oxygen gas. But there are signs that there was some oxygen around. Geochemists, for example, have found mineral deposits dated to about 3 billion years ago that they argue could only have formed in the presence of oxygen. And some evidence suggests cyanobacteria, the earliest photosynthetic organisms to release oxygen gas as a waste product—although not use it—may have arisen as early as 3.5 billion years ago.

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