Anyone that has read Hancock knows that he does not believe aliens were involved in building Earth’s impossibly complex ancient structures - and he cites the Giza pyramid as only one example. The blocks at Balbek and the complex at Golbeki Tepi are, to him, far more interesting
Yes, the Younger Dryas, when the Ice Age came back for a thousand years. Its way more recent, and came on faster, than we like to think.
Its pretty hard to prove a pre-existing advanced civilization though, as civilized remnants from even @10-11,000 years ago, well into the Holocene, are very thin on the ground (Gobekli Tepe is the most significant one). There are no known megastructures from even then.