Something happened 6,000 years ago, or thereabouts, when mankind suddenly went from inhabiting jungles to constructing monoliths. Just saying.
Agriculture.
Was that before or after the Hanging Gardens of Babylon were built?
Mankind DID start to signal *somebody* with the pyramids, Nazca lines, etc. thousands of years ago. Out of fear, hope?
I can’t see aliens as a good thing. We have our own, anyway, like Valerie Jarrett.
Longer ago than that.
At least twice as long.
Oh, humans were big into construction long before 6000 years. And have you ever heard of vimanas?
The transition of man from cromagnun to modern man took about 150 thousand years give or take. What changed man and why is still up for conjecture. The book “Them + Us” gives one possible and compelling answer, Neanderthal Predation theory. I like this book.