Life could use oxygen long before it was abundant

doi:10.1126/science.371.6533.974

GSTDTAP > 气候变化

DOI	10.1126/science.371.6533.974
	Life could use oxygen long before it was abundant
	Robert F. Service
	2021-03-05
发表期刊	Science
出版年	2021
英文摘要	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, because by tracking protein evolution, it offers a new way to reconstruct some of life's most consequential transformations. “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 largely devoid of oxygen gas—but perhaps not completely. 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 genetic analyses of photosynthetic cyanobacteria, which release oxygen gas as a waste product, suggest they may have arisen as early as 3.5 billion years ago. Yet skeptics have argued that if oxygen producers and users came along that early, they would have spread quickly across the globe. That's because using oxygen allows organisms to extract more energy from their food. But the Great Oxidation Event, which left sediments around the world filled with red bands of iron oxides, didn't occur until about 2.4 billion years ago. In the new study, Dan Tawfik, a biological chemist at the Weizmann Institute of Science, and his Ph.D. student Jagoda Jabłońska decided to look for clues in present-day microbes. They analyzed the genomes of hundreds of organisms thought to be descendants of Earth's earliest bacteria and archaea. That allowed them to create an evolutionary family tree from the genes for some 700 enzymes that either use or generate oxygen, which they divided into 134 protein families based on structural similarities. Then, they turned to a long-used approach that tracks the likely mutation rate of proteins to construct a “molecular clock.” The clock enabled them to pin down when the protein families likely evolved, dating 36 with high confidence. “We saw something quite striking,” Tawfik says: a “clear burst” of microbes using and producing oxygen between 3 billion and 3.1 billion years ago. Twenty-two of the 36 families appear to have emerged at that time, the team reported last week in Nature Ecology & Evolution . Overall, the analysis suggests that about 3.1 billion years ago, an organism (or more likely a collection of organisms) they dub the last universal oxygen ancestor emerged. Ultimately, the ability to use oxygen gave rise to aerobes that could take advantage of the increased energy output that oxygen use enabled. Eventually, those pioneers with their innovative way of life led to eukaryotic microbes that have a cell nucleus, multicellular organisms, animals, and us. The new timeline suggests early oxygen producers and users didn't immediately sweep the planet, the researchers say. Rather, they likely evolved in small pockets that slowly spread over hundreds of millions of years. Only when they became abundant enough did these organisms modify Earth's environment enough to lead to the Great Oxidation Event. “I feel like an archaeologist that is opening a grave for the first time,” Tawfik says. Still, Shih and others caution that the team's dating could be off, because molecular clocks are still an evolving science. “The order of events is almost certainly robust,” says Roger Buick, an astrobiologist at the University of Washington, Seattle. “But the timing of the events may not be.”
领域	气候变化 ; 资源环境
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/316974
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Robert F. Service. Life could use oxygen long before it was abundant[J]. Science,2021.
APA	Robert F. Service.(2021).Life could use oxygen long before it was abundant.Science.
MLA	Robert F. Service."Life could use oxygen long before it was abundant".Science (2021).