The Dark Oxygen mission targets other worlds

The initial, biologically puzzling findings were published last year In Nature Geoscience. They came from several expeditions to the area of ​​the deep sea between Hawaii and Mexico, where Professor Sweetman and his colleagues sent sensors to the sea floor – about 5 km (3.1 miles) deep.

This area is part of a vast sea floor covered with naturally occurring metal nodules, which form when metals dissolved in seawater accumulate on pieces of shell or other debris. This is a process that takes millions of years.

Sensors deployed by the team repeatedly showed rising oxygen levels.

“I just ignored it because I was taught that you only get oxygen through photosynthesis,” Professor Sweetman told BBC News at the time.

Eventually, he and his colleagues stopped ignoring what they read and set out to figure out what was going on. Experiments in their lab—with nodules the team collected in beakers filled with seawater—led the scientists to the conclusion that the metal particles produced oxygen from the seawater. The knots, they found, generated electrical currents that could split (or electrolyze) seawater molecules into hydrogen and oxygen.

Then came the backlash – published online in the form of rebuttals – from scientists and seabed mining companies.

One critic, Michael Clarke of the Metals Company, a Canadian deep-sea mining company, told BBC News that criticism focused on “a lack of scientific rigor in experimental design and data collection”. Basically, he and other critics argued that there was no oxygen production—only bubbles created by the equipment during sample collection.

“We have ruled out that possibility,” replied Professor Sweetman. “But these (new) experiments will provide evidence.”

It may seem like a niche, technical argument, but multi-billion pound mining companies are already exploring the possibility of harvesting tons of these metals from the seabed.

The natural deposits they are targeting contain metals that are essential for the production of batteries, and demand for these metals is growing rapidly as many economies switch from fossil fuels to, for example, electric vehicles.

The race to extract those resources has caused concern among environmental groups and researchers. There are more than 900 marine scientists from 44 countries signed the petition, external highlighting the environmental risks and calling for an end to mining activities.

Speaking at a press conference on Friday about his team’s latest research mission, Professor Sweetman said: “Before we do anything, we need to understand the (deep-sea) ecosystem as well as possible.

“I think the right decision, as a global society, is to stop before we decide whether this is right or not.”