I've considered a similar idea...that there was something grander than we know long long ago. Unfortunately, anything that wasn't crushed by advancing ice two miles thick, was washed away when that ice melted. I know it's probably science-fiction, but I've also wondered that if an advanced culture did exist so long ago (even if it were only something pre-industrial) then might that increase the odds that not just humans, but multiple hominid groups were interacting with each other regularly. Recent discoveries have shown many of these hominids (including homo-sapiens) were around a lot longer than we thought. Some died off, some interbred with humans and some are only known theoretically after genetic analysis of certain groups. Much of this was unknown even a decade ago. I know it seems far fetched but since I've started to consider the theory, I continue to see research and discoveries that could easily support the idea.