There is evidence that we may have had advanced civilizations on earth in the distant past. These were wiped out and mankind ended up in the dark ages. The evidence that remains is being uncovered slowly and is still considered fringe archaeology. Cities and structures underwater in the med, off the coast of Japan and in the Waters off the Americas. It is interesting and means we need a way to start expanding the race off this planet and start colonizing other planets and solar systems. If we don't we are virtually guaranteed to repeat this cycle or become extinct.