I think the theory that old stuff was made by aliens is often a way to say "older civilizations weren't as good as us and so they didn't do it, it needs to have been creatures from other planets". So I personally dislike that kind of theory (not saying that's what you're saying, just that I don't like the implications I read in it).
This being said, it's possible there is life somewhere else. If it's not intelligent, it can't make it here. If it is intelligent, it should probably stay far away