This Manganese nodule from the Blake Plateau located some 3,280 feet below the Atlantic ocean has been discovered to create "dark oxygen" that may play a role in earth's oxygen cycle and a huge role in the deep oceans ecosystem as a major source of oxygen.

How they produce oxygen? The nodules split seawater into hydrogen and oxygen through a process called seawater electrolysis. This process is powered by the electric charge of the nodules, which can reach up to 0.95 volts.

Why they matter - The discovery of dark oxygen challenges the conventional view that oxygen was first produced by ancient microbes. It also raises concerns about deep-sea mining, which could damage the marine life that depends on the oxygen produced by the nodules.
Implications

The discovery of dark oxygen could reshape how we understand the planet's oxygen production systems and how life began on Earth. It could also help us understand how life might take hold on other worlds in our Solar System

These nodules are made of rare metals and are found in the deep, dark seafloor. They contain metals like cobalt, nickel, copper, lithium, and manganese, which are used in batteries.