Scientists have discovered that polymetallic nodules—metal-rich rocks scattered across the deep ocean floor—can generate oxygen in total darkness.

This process, dubbed “dark oxygen” production, occurs when these nodules emit small electric currents strong enough to split seawater molecules into hydrogen and oxygen.

This electrochemical reaction operates independently of sunlight, overturning the long-standing belief that photosynthesis is the sole source of natural oxygen generation on Earth.

The finding, based on research conducted in the Clarion–Clipperton Zone of the Pacific Ocean and published in Nature Geoscience in 2024, suggests that deep-sea life may rely on this hidden oxygen source to survive in otherwise inhospitable environments.

This discovery opens a new window into how life can be sustained in extreme conditions, not just in Earth's oceans but potentially in the subsurface oceans of distant planets and moons like Europa or Enceladus.