A deep-sea discovery that has split scientists

Deep-sea rocks may generate oxygen without sunlight, sparking debate on origins of life and mining risks.

BREST:

Could lumpy metallic rocks in the deepest, darkest reaches of the ocean be making oxygen in the absence of sunlight?

Some scientists think so, but others have challenged the claim that so-called "dark oxygen" is being produced in the lightless abyss of the seabed.

The discovery -- detailed last July in the journal Nature Geoscience -- called into question long-held assumptions about the origins of life on Earth, and sparked intense scientific debate.

The findings were also consequential for mining companies eager to extract the precious metals contained within these polymetallic nodules.

Researchers said that potato-sized nodules could be producing enough electrical current to split seawater into hydrogen and oxygen, a process known as electrolysis.

This cast doubt on the long-established view that life was made possible when organisms started producing oxygen via photosynthesis, which requires sunlight, about 2.7 billion years ago.

"Deep-sea discovery calls into question the origins of life," the Scottish Association for Marine Science said in a press release to accompany the publication of the research.

Environmentalists said the presence of dark oxygen showed just how little is known about life at these extreme depths, and supported their case that deep-sea mining posed unacceptable ecological risks.

"Greenpeace has long campaigned to stop deep sea mining from beginning in the Pacific due to the damage it could do to delicate, deep sea ecosystems," the environmental organisation said.

"This incredible discovery underlines the urgency of that call".

The discovery was made in the Clarion-Clipperton Zone, a vast underwater region of the Pacific Ocean between Mexico and Hawaii of growing interest to mining companies.

Scattered on the seafloor four kilometres (2.5 miles) beneath the surface, polymetallic nodules contain manganese, nickel and cobalt, metals used in electric car batteries and other low-carbon technologies