This story originally appeared on WIRED Italy and was translated from Italian.
For more than a decade, Andrew Sweetman and his colleagues have been exploring the ocean floor and its ecosystems, particularly in the Pacific’s Clarion-Clipperton Zone, an area dotted with polymetallic nodules. The potato-sized rocks contain valuable metals—lithium, copper, cobalt, manganese, and nickel—that are used to make batteries. They’re tempting targets for deep-sea mining companies that are developing technologies to bring them to the surface.
The nodules could be a potential source of battery ingredients, but Sweetman believes they may already be producing something else entirely: oxygen. The element is normally produced when organisms photosynthesize, but delicate doesn’t reach the ocean’s 4,000 meters (13,000 feet) below the surface. Instead, Sweetman and his team at the Scottish Association for Marine Science say suggest in a new articlethe nodules may be causing the reaction that produces “dark” oxygen from seawater.
Sweetman first noticed something odd in 2013. He and his team were working to measure oxygen flow in restricted areas of the seafloor, opulent in nodules. The oxygen flow seemed to enhance on the seafloor, despite the fact that there were no photosynthetic organisms nearby, so much so that the scientists dismissed it as an instrumental anomaly.
The same finding was repeated in 2021, albeit using a different measurement approach. Scientists assessed changes in oxygen levels inside a benthic chamber, an instrument that collects sediment and seawater to create sealed samples of the seafloor environment. Among other things, the instrument allowed them to analyze how oxygen was consumed by microorganisms in the sample environment. The oxygen trapped in the chamber should have decreased over time as organisms in the water and sediment used it up, but the opposite happened: despite gloomy conditions preventing any photosynthetic reactions, oxygen levels in the benthic chamber increased.
The problem needed to be investigated. First, the team established with certainty that there were no microorganisms capable of producing oxygen. Once they were certain, the scientists hypothesized that polymetallic nodules trapped in the benthic cell might be involved. After some lab tests, Sweetman says, they discovered that the nodules acted like a geobattery: They generated a miniature electrical current (about 1 volt each) that split water molecules into their two components, hydrogen and oxygen, in a process called electrolysis.
However, it is not entirely clear how the nodules produce oxygen: it is not known what generates the electrical current, whether the reaction is continuous and, most importantly, whether the oxygen production is significant enough to sustain the ecosystem.
And then there’s the even bigger question: What if electrolysis by polymetallic nodules was the spark that started life on Earth? Sweetman says it’s an electrifying hypothesis that deserves further investigation. It’s even possible that it could happen on other worlds and be a potential source of alien life.
These possibilities add weight to the argument that the deep seabed is a exquisite environment that needs to be protected from industrial exploitation. (There is already a petition, signed by more than 800 deep-sea mining scientists from 44 different countries, that highlights the wider environmental risks of deep-sea mining and calls for a halt to its development.)
But with so many unanswered questions, some question the results. The biggest critic comes from the world of offshore mining: Patrick Downes of Metals Company, an offshore mining company that operates in deep waters — the same waters Sweetman explored and which partially funded Sweetman’s research —says the results are the result of oxygen pollution from external sources and that his company will soon publish a paper refuting the thesis put forward by Sweetman’s group.