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

Right so, mix of things, and there’s enough to write quite a lt more to answer these questions, but in the interest of ELI5 I’m going to summarize very hard.

* We don’t know exact requirements for alien life, and while yes we only have ourselves as examples, we have good reason to think some aspects we have on earth are a hard requirement. Like how there are many ways to build a box but usually having edges and walls aren’t optional no matter the shape it takes.

* Water is a common and abundant solvent. See, one of those core things potentially 100% necessary to life are chemical reactions (a lot of them), which usually take place best when molecules can freely diffuse around each other in close proximity–such as when they’re dissolved or in solution. There’s other solvents out there that are theoretically possible for some more unusual forms of life, such as liquid ammonia and the like, but water is our safest bet, so usually that’s what people get excited about.

* Reactions also depend a good bit on temperature. When temperature is low, things tend to turn solid, AND reactions tend to not have the energy to make transitions between states. On the other side, if temperatures are too high, these states may not be stable since there’s so much available energy that crossing energetic boundaries is pretty easy. Complex molecules like those that form the building blocks of life here on earth tend to do best somewhere in the middle. So yeah: if said planet is so far from the sun that’s it’s frozen solid and gets very little energy input, you’re unlikely to find anything.