Youth is a wonderful thing. What a crime to waste it on children. - George Bernard Shaw
Question #91516 posted on 07/31/2018 10:12 p.m.
Q:

Dear 100 Hour Board,

How similar would extraterrestrial life be to life on Earth? Obviously, other planets would provide different habitats that organisms would have to adapt differently to, but would we still see some of the same common evolutionary mechanisms producing similar kinds of plants and animals? Might there be coniferous forests? Lichen? Eyes and ears? Vertebrates? Fish? Even mammals?

-curious george, wondering if somewhere there's an alien monkey who would be his friend

A:

Dear Georgie,

There is literally no way to know this. Like, we don't even know why evolution turned out the way it did on Earth, or what is ultimately possible. As Frère pointed out, we don't even know if life would have the same molecular structure.

~Anathema

posted on 08/04/2018 2:33 p.m.
Anathema is right, obviously, that there's literally no way to know this. But I suspect the asker knew that and was perhaps looking for speculation rather than hard data. Here are a few really interesting resources:

https://www.quora.com/Do-you-think-that-aliens-on-other-planets-would-have-evolved-in-much-the-same-way-humans-have-or-would-they-be-different

https://www.quora.com/Would-extraterrestrial-life-be-very-similar-to-life-on-Earth

http://www.ox.ac.uk/news/2017-10-31-aliens-may-be-more-us-we-think