There's no tangible evidence of aliens ever visiting Earth, so I'll withhold judgement about it and default on it.
I think that the vastness of space and the conditions for a space-faring civilization to exist to make it across space makes it likely that there probably have existed thousands of such civilizations, but all at short, different spans of time, none overlapping.
I think that the vastness of space and the conditions for a space-faring civilization to exist to make it across space makes it likely that there probably have existed thousands of such civilizations, but all at short, different spans of time, none overlapping.