From Noah to Atlantis: the Great Culture Clash

Starting some time around 6000 to 5800 BC, the climate of the Anatolian plateau became too cold and dry to sustain the agriculture that formed the basis of the Catal Höyük civilization. This cold dry spell lasted for about 200 years, and the plateau was essentially abandoned. Presumably, of the people some went south toward the Levant and Mesopotamia, and some went north, down 1000m to the warm and fertile shores of the Euxine lake (now the Black Sea). They left ghost towns in perfectly good condition.

David Rohl argues plausibly that the Garden of Eden was the nearly circular area bounded by mountain arcs east of Lake Van, based on the geographical descriptions in the Bible. That area is where it is thought that deliberate crop cultivation was first practiced, and would have been abandoned during the cold dry period. From there, the natural way to go would have been to follow the Tigris and the Euphrates, both of which rise in that region.