Are the lumpy metallic formations in the deepest parts of the ocean capable of generating oxygen without sunlight?
While some researchers believe this could be the case, others are skeptical of the assertion that “dark oxygen” is being created in the seabed’s lightless environment.
This finding, which was published last July in the journal Nature Geoscience, challenges long-standing beliefs about the beginnings of life on Earth and has ignited considerable scientific discussion.
The implications are also significant for mining companies eager to extract valuable metals found within these polymetallic nodules.
Scientists indicated that nodules, each roughly the size of a potato, might produce sufficient electrical current to separate seawater into hydrogen and oxygen, a process known as electrolysis.
This discovery raises questions about the prevailing theory that life began around 2.7 billion years ago when organisms started to generate oxygen through photosynthesis, which requires sunlight.
The Scottish Association for Marine Science remarked in a press release, “This deep-sea discovery challenges our understanding of life’s origins.”
Fragile Ecosystems
Environmental activists argue that the presence of dark oxygen highlights the significant gaps in our understanding of life in these extreme depths, further supporting their stance that deep-sea mining presents grave ecological risks.
“Greenpeace has been advocating against deep-sea mining in the Pacific due to the potential harm it could cause to sensitive deep-sea ecosystems,” the organization stated. “This remarkable discovery emphasizes the urgency of that call.”
The discovery was made in the Clarion-Clipperton Zone, an extensive underwater area in the Pacific Ocean between Mexico and Hawaii that has drawn interest from mining companies.
These polymetallic nodules, found on the ocean floor four kilometers (2.5 miles) below the surface, are rich in manganese, nickel, and cobalt—metals critical for electric vehicle batteries and other low-carbon technologies.
The research that led to the dark oxygen discovery received funding from The Metals Company, a Canadian deep-sea mining company looking to evaluate the ecological effects of such mining efforts.
They have strongly criticized the study conducted by marine ecologist Andrew Sweetman and his team, claiming it is riddled with “methodological flaws.”
Michael Clarke, an environmental manager at The Metals Company, told AFP that the findings “are more likely due to poor scientific methodology and unreliable science than to an unprecedented phenomenon.”
Scientific Skepticism
Sweetman’s claims have sparked significant controversy, with many in the scientific community expressing doubts or outright rejecting his conclusions.
Since the publication in July, five academic papers refuting Sweetman’s findings have been submitted for review.
“He did not provide definitive evidence for his observations and hypotheses,” said Matthias Haeckel, a biogeochemist at the GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany.
“Many questions remain following the publication. The scientific community must conduct similar experiments to either validate or disprove his claims.”
Olivier Rouxel, a geochemist at Ifremer, the French national institute for ocean science and technology, noted to AFP that “there is absolutely no consensus regarding these results.” He suggested that the oxygen detected might simply be “trapped air bubbles” in the measuring instruments.
He expressed further skepticism regarding the ability of deep-sea nodules, which are potentially millions of years old, to still generate enough electrical current, questioning, “How can a nodule that forms so slowly continue to produce electrical current?”
When contacted by AFP, Sweetman stated he was preparing a detailed response. “Debates like these are common in the scientific community and help move the conversation forward,” he said.
