Why are the conditions for alien life to evolve the same as ours? Why can’t they evolve without water, or extremely far from their sun? Is there a reason for this or is it just because our only example is ourselves?

Question

Idk if to put biology or planetary science so ye.

In: Biology

Answer 1

We think of space like “anything can exist out there”, but chemistry is the same everywhere, and the elements available to life on Earth are pretty normal for what’s available all over the place. Living things have to do a series of chemical reactions to get energy out of their “food”, and we can understand the rules that govern these to have a good idea of what’s possible in different conditions. The Earth already has a huge variety of single-celled things that use every possible chemical pathway to extract energy and live.

Water is an example of this. Stuff dissolves really easily in it, it makes tons of chemical reactions happen much more easily, and it’s plentiful and liquid at a temperature that’s reasonable for other molecules to be stable. All known life needs water for these basic reasons, and something else would have to also do what it does.

When we do find other liquids on other planets/moons, we can work out how on paper how life that uses that instead of water might work, and what the evidence for that we might be able to see. There’s plenty of hypothetical, exotic life chemistries that people have thought up, but it’s most likely that if life is out there, it’s doing something that something in Earth is doing.