2020托福听力练习：能喷射甲烷的生物（下载）

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　　The first life on Earth appeared about four billion years ago. One place these pioneering organisms may have emerged is at hydrothermal vents, deep underwater. Where unusual chemistry provided energy for primitive life-forms to survive. Life-forms like the methane-belching microbes found at the vents today.

　　Now, for the first time, researchers have found evidence of methane-producing life in similarly extreme conditions, but at the surface of the Earth — at a spring in northern California, called The Cedars. The water there is extremely basic — with a pH of 11.6. And it contains no oxygen. Not an easy place to survive.

　　Researchers tested water and sediment at the Cedars. Some samples got dosed with mercuric chloride to kill any life present. Those dosed samples produced no methane. But the samples in which microbes were allowed to survive did put out methane. Confirming that at least some of the methane at the springs is indeed biological in origin. The findings appear in the Journal of Geophysical Research: Biogeosciences.

　　The finding has implications for climate change alleviation. A geologically similar spring in Oman has been proposed as a site for carbon storage—pumping CO2 underground, where it gets incorporated in stone. But the extremophiles at The Cedars can use CO2 to make methane—an even more potent greenhouse gas. "So imagine pumping CO2 into the ground and having it come back up as methane." Penny Morrill, a biogeochemist at Memorial University of Newfoundland. "This will not necessarily happen, but it is something to be tested for before fully implementing a carbon capture and storage technology at one of these types of sites."

　　Morrill says the study's also a reminder that life is tenacious. "We should not let our biases prevent us from looking for evidence of life in what we would otherwise consider an unexpected place." Including other planets and moons.