Scientists have made an astonishing discovery in the deep darkness of the Pacific Ocean: oxygen does not come from living organisms but from a type of gravel containing minerals, raising some questions about the theory of the origin of life on Earth.
This strange “dark oxygen” was discovered more than four kilometers deep in the abyssal plain (or ocean basin) of the Clarion-Clipperton Fault Zone in the central Pacific Ocean, according to a study published Monday.
This area is an important point for underwater mining exploitation due to the presence of polymetallic nodules, which are mineral concretes rich in minerals (manganese, nickel, cobalt, etc.) that are an essential component in the manufacture of electric car batteries, wind turbines, photovoltaic panels, and mobile phones.
A ship belonging to the Scottish Marine Science Association took samples from this area, and the mission was funded by the Metals Company and UKC Bed Resources, companies interested in prospecting for these valuable nodules.
The research aimed to evaluate the impact of this excavation on an ecosystem in which the lack of light prevents photosynthesis and therefore the existence of plants, but which is teeming with unique animal species.
“We were trying to measure oxygen consumption” at the bottom of the ocean by placing sediments under covers called benthic chambers, said Andrew Sweatman, lead author of the study, published in the journal Nature Geoscience.
It would be logical to assume that the oxygen concentration in seawater trapped in this way would decrease due to its consumption by organisms at these depths.
But the opposite was observed: “Oxygen levels increased in the water above the sediment, in complete darkness. And so, without photosynthesis,” explained Professor Sweetman, head of the research group on seafloor ecology and biogeochemistry at the Scottish Association for Marine Science.
– “Batteries in the rock”
This came as such a surprise that the researchers initially thought their underwater sensors had erred.
They ran experiments on board their ship to see if the same thing was happening on the surface, by providing an incubator in the dark for these same sediments and the nodules they contained. And again, they found that oxygen levels increased.
“We found on the surface of the nodules an electrical potential almost as high as that of an AA battery,” said Professor Sweetman, likening the nodules to “batteries in rocks.”
These amazing properties could be the result of electrolysis, which splits water molecules into hydrogen and oxygen using an electric current, a statement from the Scottish Association for Marine Science, which accompanied the study, explained. This chemical reaction occurs at 1.5 volts, the voltage of a battery, which is what the nodules can reach when they are collected.
“The discovery that oxygen is produced by a process other than photosynthesis prompts a rethink of how life on Earth emerged,” said the society’s director, Professor Nicholas Owens.
The scientist explained that the “traditional” hypothesis is that oxygen “was first produced about three billion years ago by cyanobacteria, which led to the evolution of more complex organisms.”
“Life may have started somewhere other than on land, near the ocean surface,” said Professor Sweetman. “Since this process is present on our planet, it could create oxidizing habitats on other ‘ocean worlds’ such as Enceladus or Europa (moons of Saturn and Jupiter)” and provide the right conditions for extraterrestrial life to emerge.
Sweetman hopes his findings will lead to “better regulation” of deep-sea mining, based on more accurate environmental information.
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