The recent discovery of a deep-sea oxygen source has stunned marine researchers and may necessitate a radical rethinking across several scientific fields, including the search for extraterrestrial life. Unlike the oxygen produced by photosynthesis, this oxygen is generated by minerals on the ocean floor.

High school science classes often teach that our oxygen comes from plant photosynthesis, particularly in tropical rainforests. However, scientists have long known that this is only partly true. While plants do produce a significant portion of the oxygen we breathe, phytoplankton in oceans and lakes contribute substantially as well. In both cases, the basic process involves living organisms using sunlight to convert carbon dioxide and water into necessary molecules, producing oxygen as a byproduct. This oxygen is crucial for sustaining life on Earth, including human life.

In the deep ocean, where sunlight is absent, oxygen is scarce, and marine life depends on the minimal amounts available. Previously, it was believed that the only oxygen present at depths beyond a few hundred meters was a result of ocean mixing, making any reduction in mixing rates a serious concern.

However, Professor Andrew Sweetman of the Scottish Association for Marine Science made an unexpected discovery while sampling the Clarion-Clipperton Zone, a deep-sea mountain range in the Pacific Ocean. Chambers placed on the seabed at depths exceeding 4,000 meters (13,000 feet) showed a rise in oxygen levels over several days. “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 explained. “We would come home and recalibrate the sensors, but, over the course of 10 years, these strange oxygen readings kept showing up.” The team only accepted their results after employing a different method of oxygen detection.

Sweetman and his colleagues termed this oxygen “dark oxygen” due to its unknown source and production in the absence of light. The implications of this discovery are profound. “For aerobic life to begin on the planet, there had to be oxygen, and our understanding has been that Earth’s oxygen supply began with photosynthetic organisms,” Sweetman stated. “But we now know that there is oxygen produced in the deep sea, where there is no light. I think we, therefore, need to revisit questions like: Where could aerobic life have begun?”

While the evolutionary implications of dark oxygen are significant, the immediate challenge was determining its source. After ruling out biological explanations, the team suspected polymetallic nodules, which are mineral deposits coveted by mining companies, might be responsible. Consulting with Professor Franz Geiger of Northwestern University, who had demonstrated that rust and seawater could produce electricity, the team concluded that metals on the seafloor were performing natural electrolysis, splitting water into oxygen and hydrogen.

Nodules collected and brought to Geiger’s lab were found to produce up to 0.95 volts of electric charge. In the right orientation, multiple nodules can generate higher voltages, potentially exceeding the 1.5-volt threshold needed to split seawater. “It appears that we discovered a natural ‘geobattery,’” Geiger said. “These geobatteries are the basis for a possible explanation of the ocean’s dark oxygen production.”

This discovery opens new avenues for understanding the origins of aerobic life and the potential for life in environments previously considered inhospitable.

By Impact Lab