Huh? We have plenty of fossil evidence from, from your example, a million year old hominids. Far more than we would need to expect to see evidence of civilizat

Huh? We have plenty of fossil evidence from, from your example, a million year old hominids. Far more than we would need to expect to see evidence of civilization. Subduction makes up for a tiny tiny proportion of where coastal land "goes" in any age. You'd need an enormous set of coincidences for a past civilization of hominids to go unnoticed.