system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 why finding the same gas etc on another planet is potential for another life form

There was some gas found on Venus that penguins have in their gut, which scientists are excited about because it means there's potential for a life form. But in an environment that is SO different to ours, why is it that the scientists think that life forms will need the same form/nutrients/gas etc as us? Would it not be that life forms as known on Earth, and maybe Venus Mars, every other planet would be unique and completely different to other planets, bc how different each atmosphere and environment is?

Edit: Thanks heaps for all the comments! It's more fun than googling. And also thanks heaps for my first award!
gpt
There are certain molecules that only (or usually only) come into existence by certain processes. If we find a molecule that is only generated by biologic processes, then it's a good sign that something is living in there. We could be wrong, and that molecule ended up being generated in a non-biologic way, but that's why we need to investigate further.