Until recently, little was known about oxygen’s abundance in the atmosphere [when] microbes were the only life on the planet. Now geologists doing fieldwork in northern Canada have confirmed for the first time that oxygen was extremely scarce.
The fact that life flourished amid such low oxygen levels presents a problem for scientists hunting for extraterrestrial life. The presence of the gas in the atmosphere of a planet is considered a telltale sign that it could harbor life, explains Noah Planavsky, a biogeochemist at Yale University.
But if environments with extremely low oxygen concentrations can still support life, space telescopes designed to detect an abundance of the gas may never find such life. “Even [if such planets are] teeming with complex life, they may appear—from a remote detectability point of view—as dead planets,” Planavsky says.
Planavsky and his team tested rocks for concentrations of the element cerium, which serves as a proxy for ancient oxygen levels. Oxygen binds to cerium in seawater and removes it, leaving less cerium behind to be deposited in sedimentary rock. The measured cerium levels correspond to oxygen concentrations of about 0.1 percent of present atmospheric levels, the team reported.
Such hard data, Planavsky says, should help inform the construction of the next generation of telescopes designed to hunt for life on other worlds.
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