Not this "erased from history" crap again. There was no grand ancient civilization that existed and was wiped out before the Sumerians came around 4,000 BCE. You know how we know? Because 1) there would be archaeological evidence and there is none 2) they would have had to invent agriculture and that would've left evidence behind via genetics in modern plants of human-guided cultivation 3) they would have used all the same energy resources we have, so timber, peat, coal, oil, etc. and that would have significantly altered the environment in such a way as to leave a record - not to mention it would mean there would be no coal or oil left for us and 5) we have archaeological evidence of early humans during this time - and they were hunter/gatherers leading basic subsistence lives as evidenced by the wear on their bones and teeth and the radioactive signatures in their bones of what they ate.

So why did it take almost all of the last 100,000 years for civilization to happen? Because without the stability provided by agriculture, doing anything more than surviving is really fucking hard. Not to mention the repeated ice ages and other things that made long term progress impossible.