In a remarkable discovery that could reshape our understanding of Earth's history and the origins of life, scientists have found evidence of oxygen production in the lightless depths of the Pacific Ocean.
This finding, published in Nature Geoscience, challenges the long-held belief that all Earth's oxygen is generated through photosynthesis.
A team led by Prof Andrew Sweetman of the Scottish Association for Marine Science (SAMS) made the discovery while conducting research in the Clarion-Clipperton Zone between Hawaii and Mexico, approximately 4,000 metres below the ocean surface.
“When we first got this data, we thought the sensors were faulty because every study ever done in the deep sea has only seen oxygen being consumed rather than produced,” Sweetman said.
“We would come home and recalibrate the sensors but over the course of 10 years, these strange oxygen readings kept showing up.”
The team dubbed the phenomenon “dark oxygen” owing to the fact that light cannot penetrate at this depth – a suitable name given its mysterious origins.
So where is the oxygen source coming from?
The researchers were there to assess the potential impacts of deep-sea mining operations looking to extract materials from polymetallic nodules. These mineral concentrations on the ocean floor contain precious metals essential for the lithium-ion batteries that power electric vehicles and phones.
The results show that the nodules carry a high electric charge which could be capable of splitting seawater into hydrogen and oxygen via a process known as seawater electrolysis.
“Through this discovery, we have generated many unanswered questions and I think we have a lot to think about in terms of how we mine these nodules, which are effectively batteries in a rock,” Sweetman said.
SAMS Director Prof Nicholas Owens called the discovery "one of the most exciting findings in ocean science in recent times," adding that it "requires us to rethink how the evolution of complex life on the planet might have originated."
The conventional view that oxygen was first produced by ancient microbes called cyanobacteria around three billion years ago may now need to be reevaluated.
This alternative source of oxygen production could lead to a "radical rethink" of how complex life developed on Earth, Owens said.
Furthermore, these results add weight to calls from those looking to protect deep ocean habitats from the potentially damaging effects of deep sea mining – a practice the US National Oceanic and Atmospheric Administration (NOAA) has warned: “could result in the destruction of life and the seabed habitat in the mined areas”.
If the nodules are responsible for oxygen production, their removal may not only disrupt the environment but could wipe out a vital oxygen supply to the creatures that call this alien world home.
“I don't see this study as something that will put an end to mining,” Sweetman explained in an interview with BBC News, “[But] we need to explore it in greater detail and we need to use this information and the data we gather in future if we are going to go into the deep ocean and mine it in the most environmentally friendly way possible.”
About the experts
Andrew Sweetman is the leader of the Seafloor Ecology and Biogeochemistry research group at the Scottish Association for Marine Science, UK. He holds a PhD in deep-sea ecology from the Max Planck Institute for Marine Microbiology. Over the last 12 years, he has generated £10 million of research funding and led/co-led 27 research projects.
Nicholas Owens is a marine scientist with experience in leadership of complex organisations engaged in research, commercial income generation and education in environmental science. He is currently the director of the Scottish Association for Marine Science.
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