Earth’s oxygen is something of a puzzle. Until recently, scientists believed it is produced entirely by photosynthesis — plants using sunlight to convert carbon dioxide and water into glucose and oxygen.
But earlier this year, oceanographers discovered an entirely new source of oxygen. Deep in Earth’s oceans, they found oxygen levels much higher than can be explained by photosynthesis alone, which typically occurs near the surface where sunlight can penetrate.
The researchers concluded that the oxygen must be produced in the deep ocean itself, probably as a result of an electrochemical reaction between metal nodules on the ocean floor and seawater. In other words, without sunlight at all.
