Scientists may have discovered 'dark oxygen' being created without photosynthesis

Researchers scouring the lightless landscape of the Pacific Ocean floor think they've observed "dark oxygen" being created there, potentially challenging commonly held beliefs 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.

"I think we therefore need to revisit questions like: where could aerobic life have begun?" said Andrew Sweetman, a professor with the Scottish Association for Marine Science in Oban, Scotland, in a news release.

The research team led by Sweetman published its findings Monday in an article in the journal Nature Geoscience.

The scientists aren't certain how oxygen is created at such dark depths, but they believe it's being produced by electrically charged minerals called polymetallic nodules, which range in size from a small particle to about the dimensions of a potato.

These nodules — "effectively batteries in a rock," Sweetman said — may use their electric charge to split seawater into hydrogen and oxygen in a process called seawater electrolysis.

"The conventional view is that oxygen was first produced around three billion years ago by ancient microbes called cyanobacteria and there was a gradual development of complex life thereafter," said the director of the Scottish Association for Marine Science, Nicholas Owens, in the news release. "The potential that there was an alternative source requires us to have a radical rethink."

Researchers conducted tests on the seafloor and also collected samples to test aboveground, and they came up with the same result: that oxygen levels increased near the polymetallic nodules.

Seawater can be split into hydrogen and oxygen with 1.5 volts of electricity, which is the amount in a AA battery. Researchers found that some of the nodules possessed as much as 0.95 volts of electricity, and multiple nodules together produced even higher voltages.

The discovery could impact deep-sea mining

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

Franz Geiger, a Northwestern University chemistry professor 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 demands for decades after.

But he also said that mining would have to be conducted in a way that did not eliminate oxygen for life forms in that part of the ocean.

"We need to be really careful if it turns out that deep-sea mining will become an opportunity that's being pursued … that's done on a level and at a frequency that is not detrimental to life down there," Geiger told NPR.

Companies conducted exploratory missions for deep-sea mining in the 1970s and '80s, he said, and recent research suggests that those missions may have had repercussions on marine life in the area for decades.

"A few years ago, a team of marine biologists went back to those areas that were mined 40 years ago and found essentially no life," Geiger said. "And then a few hundred meters over to the left and right, where the nodules were intact, plenty of life."