New Delhi, India

Researchers have found that metallic minerals on Earth's deep-ocean floor are causing chemical reactions that're leading to the production of mysterious "dark oxygen", which has bewildered scientists.  

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In a study published on Monday (Jul 22) in the journal Nature Geoscience, a team of international researchers, including a chemist, discovered that oxygen is being created without the involvement of life. 

The findings of the study refute long-held beliefs that only photosynthetic creatures, including plants and algae, can produce oxygen on Earth. The study titled, "Evidence of dark oxygen production at the abysmal seafloor", suggests that there may be another way also. 

It seems that oxygen can also be created at the seafloor, where light cannot reach, to sustain the oxygen-consuming (aerobic) marine life that survives in total darkness. 

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As reported by phys.org, Andrew Sweetman, of the Scottish Association for Marine Science (SAMS), made the "dark oxygen" discovery while conducting ship-based fieldwork in the Pacific Ocean. Northwestern's Franz Geiger led the electrochemistry experiments, which potentially explain the finding. 

During fieldwork in 2013, Sweetman and his collaborators first noticed it. The researchers studied sea-floor ecosystems in the Clarion–Clipperton Zone, which is a potential target for the mining of metal-rich nodules. They first thought that something was wrong with their equipment. But similar readings kept showing on the sensors in other attempts as well. 

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As quoted in the report, Sweetman said, "For aerobic life to begin on the planet, there had to be oxygen, and our understanding has been that Earth's oxygen supply began with photosynthetic organisms." 

"But we now know that there is oxygen produced in the deep sea, where there is no light. I think we, therefore, need to revisit questions like: Where could aerobic life have begun?" said Sweetman, who leads the Seafloor Ecology and Biogeochemistry research group at the Scottish Association for Marine Science (SAMS). 

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Sweetman said that this is one of the "most exciting findings" in ocean science in recent times. 

The researchers found that black and rounded rocks pepper the floor in the midst of the Pacific Ocean. 

As per the measurements done by the scientists, oxygen levels have been increasing slowly at depths of more than 4,000 metres (13,000 feet). 

"When we first got this data, we thought the sensors were faulty, because every study ever done in the deep sea has only seen oxygen being consumed rather than produced. We would come home and recalibrate the sensors but over the course of 10 years, these strange oxygen readings kept showing up," explained Sweetman.

"We decided to take a back-up method that worked differently to the optode sensors we were using, and when both methods came back with the same result, we knew we were onto something ground-breaking and unthought-of," he added. 

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The key to the discovery is found in polymetallic nodules, which are naturally occurring mineral deposits that grow on the ocean floor. The nodules are a mixture of several minerals. They range in size from microscopic particles to a typical potato. 

"The polymetallic nodules that produce this oxygen contain metals such as cobalt, nickel, copper, lithium and manganese—which are all critical elements used in batteries," said Geiger, who co-authored the study.

"Several large-scale mining companies now aim to extract these precious elements from the seafloor at depths of 10,000 to 20,000 feet below the surface. We need to rethink how to mine these materials, so that we do not deplete the oxygen source for deep-sea life," Geiger added. 

(With inputs from agencies)