Metallic pebbles, potato-sized nodules, are scattered across the floor of the Pacific Ocean. But what is surprising is their ability to produce oxygen in complete darkness, without any aid from living organisms, according to new research.
Polymetallic nodules formed millions of years ago and grow at a rate of 0.08 inches (2 millimeters) per million years.
Credit: DeepCCZ expedition
Discovering oxygen produced without biological intervention, named "dark oxygen," disrupts our understanding of how terrestrial life emerged. Researchers initially thought their sensors were flawed, as they are more accustomed to observing oxygen consumption in the depths of the ocean.
Andrew Sweetman, head of the study and professor at the Scottish Association for Marine Science (SAMS), explained that their instruments consistently revealed oxygen production. The results, published in
Nature Geoscience, indicate that these North Pacific nodules produce oxygen through the electrolysis of seawater, due to an electric potential between the metal ions.
Abyssal plains, situated between 9,800 and 19,700 feet (3,000 and 6,000 meters) deep, are abundant with these nodules composed mainly of iron and manganese oxides, but also containing cobalt, nickel, lithium, and rare earth elements like cerium, which are essential for electronic and low-carbon technologies.
Sweetman and his team initially studied the potential impact of mining these nodules in the Clarion-Clipperton Zone (CCZ), which spans 1.7 million square miles (4.5 million square kilometers) between Hawaii and Mexico. Oxygen measurements taken with experimental chambers revealed constant emissions from the seabed, contradicting the expectation of decreasing oxygen with depth.
Polymetallic nodules are aggregates composed of iron and manganese oxides, also containing valuable metals such as cobalt and rare earth elements.
Credit: NOAA Office of Ocean Exploration and Research, 2019 Southeastern U.S. Deep-sea Exploration
This discovery challenges the notion that terrestrial oxygen originates solely from photosynthesis, raising new questions about life's origin around 3.7 billion years ago. If life requires oxygen to begin, this abyssal production offers a new perspective on possible locations for the emergence of aerobic life.
Finally, this revelation raises concerns about the mining of polymetallic nodules. These "natural batteries" could be crucial to the deep-sea ecosystem, and their extraction might have significant ecological consequences.