Ground-breaking discovery of 'dark oxygen' in depths of Pacific Ocean baffles scientists

The conventional belief about oxygen is that it was first produced billions of years ago by ancient microbes called cyanobacteria in the process of photosynthesis, in which plants and other living organisms convert carbon dioxide and water into oxygen. However, when Professor Andrew Sweetman investigated the dark depths of the Pacific Ocean, he found something that challenged this long-held view. In the oceanic depths, real oxygen was bubbling over the seabed, without the aid of any sunlight or organisms. At first, he didn’t believe what he saw, but when he came across the idea of “batteries in rocks,” he had to believe it, reported CNN. Recently, he published a study about his findings in Nature Geoscience.

Sweetman, from the Scottish Association for Marine Science (SAMS), first noticed this bizarre oxygen-production phenomenon in a 2013 expedition. He dangled a shoe-box-sized deep-ocean lander into the seafloor and was so disappointed by his finding that he didn’t believe it. Instead, he thought that the monitoring equipment was faulty. “I basically told my students, just put the sensors back in the box. We’ll ship them back to the manufacturer and get them tested because they’re just giving us gibberish,” Sweetman told CNN, “And every single time the manufacturer came back: ‘They’re working. They’re calibrated.’”

After this expedition, Sweetman ventured on three subsequent expeditions in the same region. He investigated the Clarion-Clipperton Zone between Hawaii and Mexico, approximately 13,000 feet (4,000 meters) deep into the Pacific Ocean. At such depths, sunlight cannot reach by any means and hence, there was no possibility of finding oxygen there. But in each expedition Sweetman undertook, the sensors detected signs of oxygen. He dubbed it “dark oxygen,” given the dark environment of the seafloor where it was being puffed out. But he was still puzzled wondering what could be the source of this mysterious oxygen.

He had stumbled upon these oxygen bubbles almost unexpectedly and he kept observing it time and time again. His initial goal behind these expeditions was to assess the marine biodiversity that is typically designated for mining potato-size polymetallic nodules. These nodules, strewn across the seafloor, are formed by chemical processes over millions of years. The water that swishes past things like shell fragments, squid beaks and shark teeth, accumulates metal flakes, and over time, forms these metal nuggets. These metals including cobalt, nickel, copper, lithium, and manganese are then used to build electric batteries and a variety of electronics.

But when he repeatedly came across oxygen deep down there, he was determined to find what was causing it. After collecting samples of sediment, seawater, and polymetallic nodules, he returned to his laboratory and set out to discover how this “dark oxygen” was being produced without sunlight or living organisms. Then, one day, as he was sitting in a Brazilian hotel, watching a documentary, he heard someone say the phrase “battery in a rock.” A lightbulb went on in his head. He wondered whether the mysterious oxygen was being produced by an “electrochemical” process.

There is a process called “seawater electrolysis.” When electric current is passed through seawater, it splits the water into oxygen and hydrogen. Sweetman thought that a similar process was going on inside the metallic nodules. He reached out to electrochemist Franz Geiger, who was equally flabbergasted. “It appears that we discovered a natural ‘geobattery,’” said Geiger, per CNN. “These geobatteries are the basis for a possible explanation of the ocean’s dark oxygen production.”

So the answer to the question “Where is this dark oxygen coming from,” turned out to be “metal.” The remarkable finding can change the way scientists think about the origin of life. Plus, if these metal nuggets produce oxygen, the world now has a new supply of oxygen, which is cool. "The discovery of oxygen production by a non-photosynthetic process requires us to rethink how the evolution of complex life on the planet might have originated," said SAMS marine scientist Nicholas Owens, per ScienceAlert. "In my opinion, this is one of the most exciting findings in ocean science in recent times."

This also raises concerns that potential mining processes could end up destroying these vital supplies of oxygen as they pierce into these metallic nuggets, nearly smattering them to powder. But as far as curiosity is concerned, scientists have found a melting pot of gold to contemplate the origin of life. "We now know that there is oxygen produced in the deep sea, where there is no light," said Sweetman per ScienceAlert. "I think we, therefore, need to revisit questions like: Where could aerobic life have begun?"