Scientists have discovered "dark oxygen" being produced in the deep ocean, apparently by lumps of metal on the seafloor.
About half the oxygen we breathe comes from the ocean. But, before this discovery, it was understood that it was made by marine plants photosynthesising - something that requires sunlight.
Here, at depths of 5 km. (approx. 3.1 miles), where no sunlight can penetrate, the oxygen appears to be produced by naturally occurring metallic “nodules” that split seawater - H2O - into hydrogen and oxygen.
Please select this link to read the complete article from The BBC.