The Younger-Dryas period was from about 13.000 years ago to 11,500 y_a. Our Earth took heavy destruction and plunged into a short Ice-age that lasted for about 15 centuries (ocean levels dropped 400 ft). Survivors settled the new lower coastline. But at its end, the planet suffered another catastrophe like the heat from a mega solar-flare, which ended this Ice-age (and sea level rose quickly again destroying costal cities in a great flood). The Pyramids and Gobekle-Tepe are stone structures from that time -- of 11,500 years ago.