'Dark oxygen' discovery upends centuries of scientific beliefs, textbooks to be rewritten

Scientists recently reported an unexpected deep-sea development in the Pacific: certain metallic rocks seem to be making oxygen in the dark, without light or sunshine, at the bottom of the ocean.

This idea runs counter to the usual belief that oxygen only forms in sunlight through photosynthesis.

Although these findings have stirred debate, the central claim is that potato-sized nodules found thousands of feet below the surface appear to split seawater molecules and release oxygen.

Oxygen and photosynthesis – the basics

Since the late 1700s, we’ve been taught that light creates oxygen through photosynthesis, a crucial natural process that keeps life on Earth thriving.

Plants, algae, and some bacteria soak up sunlight to turn carbon dioxide and water into glucose and oxygen.

In the simplest of terms, nature uses light as fuel to produce the oxygen we breathe and keep everything on Earth alive.

Photosynthesis not only gives energy to these organisms but also releases oxygen into the atmosphere, maintaining the perfect balance of gases that most life forms need.

Until the discovery of dark oxygen, it has been commonly accepted knowledge that without light, photosynthesis would grind to a halt, and our planet wouldn’t have the oxygen-rich air we rely on every day.

Deep-sea rocks making oxygen

Exploration in a region called the Clarion-Clipperton Zone – where deep-sea mining companies are eyeing metals resources like cobalt and nickel – uncovered ferromanganese nodules resting on the ocean floor.

Ferromanganese nodules are like little treasure rocks that settle on the ocean floor, packed with metals such as manganese and iron.

These nodules form slowly over millions of years as minerals from seawater build up in layers around a tiny core, like a shark tooth or a piece of shell.

Think of them as underwater onions, with each layer adding more minerals and creating these cool, rounded shapes.

Researchers suggested that the nodules may produce electric charges that spark electrolysis, generating oxygen and hydrogen.

How do the rocks produce oxygen?

Early studies raised plenty of questions about the process and the potential effect on seafloor life.

Leading the push for more answers is Andrew Sweetman, a professor at the Scottish Association for Marine Science. 

He is running a three-year project to investigate how these nodules might form oxygen in the absence of light. One of his goals is to see if this phenomenon appears in other parts of the Clarion-Clipperton Zone. 

“Our discovery of dark oxygen was a paradigm shift in our understanding of the deep sea and potentially life on Earth, but it threw up more questions than answers,” said Sweetman.

He and his team will also look into whether microbial reactions help release hydrogen, an energy source for certain deep-sea microbes.

Freshwater mysteries

Dark oxygen has popped up in other surprising, light-deprived places.

Emil Ruff detected oxygen in freshwater samples beneath Alberta, Canada. It appeared in groundwater that had been isolated for tens of thousands of years, yet still contained enough oxygen to support life. 

“After 40,000 years or 30,000 years (separated from surface processes), there’s no reason really to think that there should be any oxygen left,” remarked Ruff.

He found that special bacteria could produce oxygen on their own by breaking down certain dissolved compounds.

What’s more, Ruff found that the quantity of oxygen produced was enough to sustain other oxygen-dependent microbial life in the groundwater.

Challenging dark oxygen

Not all scientists are in agreement about this dark oxygen discovery. Some deep-sea mining interests challenged Sweetman’s work, saying they have found no such electrical oddities in the nodules.

The Metals Co. submitted a rebuttal of the scientific research paper to Nature Geoscience, which awaits peer review.

Meanwhile, independent observers note the need for more experiments. A research oceanographer at the US Geological Survey’s Pacific Coastal and Marine Science Center in Santa Cruz, California, said the USGS has not observed any electrical phenomena in ferromanganese nodules examined so far.

She was not involved in either Sweetman’s or Ruff’s research.

NASA hopes these findings might hint at life in places beyond Earth. Dark ocean worlds like Jupiter’s moon Europa and Saturn’s moon Enceladus are prime targets for research.

Sweetman shared that the space agency wants to test whether high pressures found on those icy moons can trigger oxygen generation in deep-sea rocks without direct sunlight. If the same basic chemistry works there, it could point to possible microbial life in alien seas.

Dark oxygen and deep-sea mining

The Clarion-Clipperton Zone sits far offshore, and mining there is governed by the International Seabed Authority. Critics argue that removing nodules in huge volumes could destroy habitats.

Organizations like Fauna & Flora warn of irreparable harm, saying it may disturb carbon storage in the ocean. Sweetman believes it is risky to harvest seabed minerals until scientists know a lot more about these systems.

He acknowledges the controversy and plans to address critics in peer-reviewed forums. For now, the hunt for hard data continues, fueled by the hope of expanding our understanding of life – both here and possibly on other worlds.

The study is published in Nature Geoscience.

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