I don’t know how everything happened. But I know that men concerned with Knowledge and aware of the import of findings and discoveries, find ways to preserve and protect those.
(And I don’t think we need ‘Outer Space Visitor’ stories, to explain human accomplishment on Earth.)
No, I don’t think so either.
It is interesting to me who the same structures pop up in Africa, South America, and on out into the Pacific.
I suspect possible tectonic shifts to answer for part of it.
Not sure if that’s even possible considering the time frames, but possibly.
At any rate, I agree with your premise.