A biggest open question to me is how universal is "organic chemistry". Science says YES, but we don't know. Who when asked about whether there was life elsewhere in the universe, answer "If not, its a damn waste of space?" But given that unavoidable huge waste of space, we all accept "complex life will be different everywhere", but will simple life also be different everywhere? At what point does biochemistry evolution diverge? And we don't even understand what viruses are, or how they developed separate but compatible with us. Perhaps viruses COULD interact with alien life, and evolve to work with it, while nothing else could.