Beneath the ocean waves, there’s a complex world that we’ve only explored a fraction of . In its dark depths, a discovery revealed this week may turn our knowledge of how life began on its head.
Researchers from the Scottish Association for Marine Science (SAMS) published a study this Monday in the Nature Geoscience journal that aimed to investigate how deep-seafloor organisms consume oxygen and the role that naturally occurring metallic treasure plays in the process. They call their discovery “dark oxygen.”
We know that, on land, plants use energy from sunlight to perform photosynthesis and create oxygen. What’s less clear how this occurs in the deep ocean, at levels further than where sunlight can travel. This is where dark oxygen comes in.
Most of the seafloor is around 2.5 miles below the ocean surface, which is too deep for sunlight to penetrate. Some parts, including canyons and trenches, are even deeper, per the National Oceanic and Atmospheric Administration . Water already doesn’t have very much oxygen available, according to the National Park Service . It only takes up about 1% of water’s volume.
“For aerobic life [organisms that live off oxygen] to begin on the planet, there had to be oxygen and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” said Prof. Andrew Sweetman of SAMS. He led the team that made the deep ocean discovery while doing ship-based fieldwork in the Pacific Ocean. “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?”
Specifically, the team made their discovery in the Clarion-Clipperton Zone, an abyssal plain as wide as the continental U.S., spanning 1.7 million square miles between Hawaii and Mexico. They were there to assess the impacts of deep-sea mining.
“Lying atop the muddy bottom or embedded just beneath it are trillions of potato-size polymetallic nodules,” said Pew Charitable Trusts of the Clarion-Clipperton Zone. “These rocklike deposits contain nickel, manganese, copper, zinc, cobalt, and other minerals.”
Some of these materials are used to produce lithium-ion batteries for electric vehicles and mobile phones, SAMS explained in a press release.
While conducting experiments, Sweetman’s team found nodules that carried a very high electric charge. These charges could be powerful enough to split the seawater into hydrogen and oxygen through a process called seawater electrolysis.
“Only a voltage of 1.5 V is needed for seawater electrolysis to occur – the same voltage as a typical AA battery,” said SAMS. “The team analyzed multiple nodules and recorded readings of up to 0.95 volts on the surfaces of some, meaning that significant voltages can occur when the nodules are clustered together.”
At first, the researchers thought their sensors were faulty. However, after recalibrations and a decade of strange oxygen readings, they had to give the data a closer look. They used a different type of sensor and got the same results.
Now, Sweetman is looking to conduct more research into “dark oxygen” production and its relationship to deep sea mining. Even though the discovery does seem to solve one mystery, it has also generated many more unanswered questions, especially about the nodules, he said, referring to them as “effectively batteries in rock.”
“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 Director Prof. Nicholas Owens. “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.”
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