Science Focus - the home of BBC Science Focus Magazine
Could alien life breathe a gas other than oxygen? © iStock

Could alien life breathe a gas other than oxygen?

Subscribe to BBC Science Focus Magazine and get 6 issues for just £9.99

Breathing sulphur sounds cool but it would get old breathing air that smells of rotten eggs!

Asked by: Aaron Cottingham, Chiddingly


Free oxygen is so reactive that it doesn’t last long in the atmosphere unless plants and other photosynthetic organisms continuously replenish it. This means that on any planet, including Earth, life must initially evolve without any oxygen to breathe.

There are lots of modern bacteria that ‘breathe’ many other elements and compounds, including sulphur, carbon dioxide, iron, manganese, cobalt and uranium. All of these are much less common in the Universe than oxygen though, which is the third most common element.

There are bacteria that can metabolise hydrogen gas, which is the most abundant element, but like all of these alternative metabolisms, it is much less efficient than oxygen-based systems. This might mean that simple bacterial life is common across the galaxy using lots of different biochemistries, but complex multicellular life only evolves where it has access to the boost in energy provided by oxygen reactions.

Read more:


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.


luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.


Sponsored content