In the depths of the Pacific Ocean and in total darkness, scientists have discovered with astonishment oxygen coming not from living organisms but from a kind of pebble containing metals, which questions the theory on the origins of life on Earth.
This strange “black oxygen” was detected at a depth of more than 4 kilometers, in the abyssal plain of the Clarion-Clipperton geological fracture zone, in the central Pacific, according to a study published Monday.
A prime target for underwater mining due to the presence of polymetallic nodules, mineral concretions rich in metals (manganese, nickel, cobalt, etc.) needed in particular for the manufacture of batteries for electric vehicles, wind turbines, photovoltaic panels and mobile phones.
It was in this area that a vessel from the Scottish Association for Marine Science (SAMS) carried out samples, funded by the companies The Metals Company and UK Seabed Resources, which covet these precious nodules.
Objective of the research: to assess the impact of such prospecting on an ecosystem where the absence of light prevents photosynthesis and therefore the presence of plants, but which is full of unique animal species.
“We were trying to measure the oxygen consumption” of the ocean floor, by placing its sediments under bell jars called benthic chambers, Andrew Sweetman, first author of the work published in Nature Geoscience.
Logically, the seawater thus trapped should have seen its oxygen concentration decrease, as the latter was consumed by living organisms at these depths.
However, the opposite was observed: “the oxygen level increased in the water above the sediments, in complete darkness and therefore without photosynthesis”, explains Professorr Sweetman, head of the SAMS Seafloor Ecology and Biogeochemistry research group.
Piles in the rock
The surprise was such that the researchers initially thought their underwater sensors had made a mistake.
They conducted experiments on board their ship to see if the same thing happened on the surface, by incubating the same sediments and the nodules they contained in the dark. And they found once again that the oxygen level increased.
“On the surface of the nodules, we detected an electrical voltage almost as high as in an AA battery,” describes Professor Sweetman, comparing these nodules to “batteries in the rock.”
These astonishing properties could be at the origin of a process of electrolysis of water, which separates its molecules into hydrogen and oxygen using an electric current. This chemical reaction occurs from 1.5 volts — the voltage of a battery — that the nodules could reach when they are grouped together, according to a press release from the SAMS association attached to the study.
“The discovery of oxygen production by a process other than photosynthesis encourages us to rethink the way in which life appeared on Earth,” linked to the appearance of oxygen, comments Professorr Nicholas Owens, Director of SAMS.
The “conventional” view is that oxygen “was first produced about 3 billion years ago by cyanobacteria which led to the development of more complex organisms,” the scientist explains.
“Life could have started somewhere other than on land and near the surface of the ocean,” says Professorr Sweetman. “Since this process exists on our planet, it could generate oxygenated habitats on other ‘ocean worlds’ like Enceladus or Europa [des lunes de Saturne et de Jupiter] ” and create the conditions for the appearance of extraterrestrial life.
He hopes his findings will help “better regulate” deep-sea mining, based on more accurate environmental information.