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Researchers studying the light-deprived landscape of the Pacific Ocean floor believe they have observed the creation of “dark oxygen,” potentially challenging conventional wisdom about how oxygen is produced on Earth.

Until now, it was thought that oxygen was created only through photosynthesis, a process that requires sunlight. But the discovery casts doubt on that theory and raises new questions about the origins of life itself.

“So I think we need to revisit questions like: where might aerobic life have started?” said Andrew Sweetman, a professor at the Scottish Marine Science Association in Oban, Scotland, in a news release.

The research team led by Sweetman published their findings Monday in a journal article Nature Geoscience.

Scientists aren’t sure how oxygen is created at such dark depths, but they think it’s produced by electrically charged minerals called polymetallic nodules, which range in size from a tiny particle to the size of a potato.

These nodules — “effectively batteries in a rock,” Sweetman said — can use their electrical charge to split seawater into hydrogen and oxygen in a process called seawater electrolysis.

“The conventional view is that oxygen was first produced about three billion years ago by ancient microbes called cyanobacteria, and then there was a gradual development of complex life,” Scottish Marine Science Association director Nicholas Owens said in a press release. “The potential that there is an alternative source requires us to radically rethink.”

The researchers conducted tests on the sea floor and also collected samples to test above ground, and came to the same result: oxygen levels rise near the polymetallic nodes.

Seawater can be split into hydrogen and oxygen with 1.5 volts of electricity, which is the amount in an AA battery. The researchers found that some of the nodules held up to 0.95 volts of electricity, and multiple nodules together produced even higher voltages.

The discovery could affect deepwater mining

Polymetallic nodules contain metals such as manganese, nickel and cobalt, which can be used to make lithium-ion batteries used in consumer electronics, appliances and electric vehicles.

Franz Geiger, a professor of chemistry at Northwestern University who worked on the study, said in a separate news release that there may be enough polymetallic nodules in an area of ​​the Pacific Ocean called the Clarion-Clipperton Zone to meet global energy needs for decades after.

But he also said mining would have to be done in a way that doesn’t eliminate oxygen for life forms in that part of the ocean.

“We have to be very careful if it turns out that deep-sea mining is going to become an opportunity that’s being pursued … it’s being done at a level and at a frequency that’s not harmful to life down there,” Geiger told NPR.

Companies conducted exploratory missions for deep-sea mining in the 1970s and 1980s, he said, and recent research suggests those missions may have had effects on marine life in the area for decades.

“A few years ago, a team of marine biologists went back to these areas that had been mined 40 years ago and found essentially no life,” Geiger said. “And then a few hundred meters to the left and right, where the nodules were intact, a lot of life.”