For most of life on Earth, oxygen is essential, and sunlight is usually needed to produce that oxygen.

Scientists have found that a microbe called Nitrosopumilus maritimus and several of its cousins, called ammonia oxidizing archaea (AOA), are able to survive in dark, oxygen-depleted environments by producing oxygen on their own.

The team wanted to take a closer look at what would happen when all the available oxygen was gone, and there was no sunlight to produce new oxygen.

What they found was something unexpected: the microorganisms produced their own oxygen to create nitrite, with nitrogen gas (dinitrogen) as a by-product.

At the moment, the researchers aren't certain how the microbes are pulling off this trick, and the amount of oxygen produced appears to be relatively small (just enough for their own survival) – but it does look to be different to the few oxygen-without-sunlight processes that we already know about.