The deep sea is home to “dark oxygen”

TIt’s wide The majority of oxygen on Earth is made as a byproduct of photosynthesis, the use of light to convert water and carbon dioxide into sugars. Any oxygen present in areas where photosynthesis is impossible – such as the abyssal seafloor, a black world up to 6,000 meters deep – was thought to be a moving surface gas.

In a paper published in Natural Earth SciencesHowever, Andrew Sweetman – from the Scottish Marine Science Society – and his colleagues have revealed that some of it is actually ‘dark oxygen’ created without sunlight.

The first indications that this gas was being produced on the deep seafloor came in 2013, when researchers noticed that oxygen levels were higher near polymineral nodules, clumpy assemblages of minerals and minerals found across the ocean floor. The researchers believe that the electric field exerted by these nodules could strip electrons from the water, freeing oxygen from its molecular prison.

This discovery suggests that aerobic (oxygen-dependent) life may have emerged before the evolution of photosynthesis. This is controversial. But dark oxygen could certainly help the aerobic microbes living in the depths today, as well as the larger organisms that eat them. ■

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