In southeast Turkey there is a obviously man-made structure that required the labor of highly skilled stone carvers that has been dated to 12,000 years ago.
Dwark, India has the remains of a city now underwater that was submerged by the rising sea 3,500 years ago and may have been build over 12,000 years ago.
Gold mines and adjacent communities in South Africa have been discovered that have been dated to 200,000 years ago which would make them almost as old as the species Homo Sapiens.
All these dates predate what was supposed to be the beginning of human civilization. According to traditional scholars mankind at the beginning of the Holocene Era were just beginning to gather into settlements. Farming and simple structures were just starting. The most advanced people were beginning to make tools out of metal (bronze) and not just stone. Still, the communities were thought to be just a gathering of nomads and the kind of organization necessary for massive building projects were thought impossible.
And at the time that gold was being mined 150 miles east of Johannesburg mankind was supposed to be hunter-gatherers less interested in digging for useless rocks than they were in downloading songs on iTunes.
Of course, these discoveries have encouraged speculation about aliens or Atlanteans. But it does suggest that human civilization is much older than we have supposed and that there is a whole chapter of human history left undiscovered.