system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why are we so certain that water and oxygen are required for alien life?

We're assuming that alien life requires the same things we do, why?
gpt
> We're assuming that alien life requires the same things we do

We aren't. There might well be alien life that doesn't require any of that. It might be strange and completely unrecognizable.

And there is the problem; if the alien life is unrecognizable then what do we look for? We only have the one example of life to work from, the life on our planet, so it makes sense to look for the kind of life that we know the signs of rather than something we don't know anything about.