[SigmundA]

Self replication of information with mutation and evolution would be my definition, which would include viruses, but not crystals, AI could be included if it could evolve on its own.

I think in reality like most things its not black and white, there is a continuum of life and some things are more alive than others.

Edit: perhaps adapting to environment through mutation/evolution or learning or both might be better.

[n4r9]

Evolution has led to life but I'm struggling to see why it should be a criterion. What if something happened that stopped humans evolving, and we maintained the same general genetic distribution for the next few millennia? Would we stop living?

[machiaweliczny]

Yes, without adaptations over time we would probably die as species. I guess that as long as universe is evolving we need to as well to survive.

Simple historic example: change of oxygen level, change of temparature is another likely event

[SigmundA]

Which is why I added the edit. The thing I consider most defining of life is its ability to adapt to its environment both through evolution and later through intelligence and learning.