[Aussie Gamer]

I am not a Biologist or anything like that but it seems a bit narrow minded to remove the possilblity of life breathing other gases.
We understand really our own biology but have not yet found life on another world to study it. This could be because yes you do need O2 or the worlds near us just suck.

Hopefully one day we get to find out that we are not alone is this universe.