7600 years ago when the fresh water Black Sea was flooded with salt water, the Caucasian irrigation farmers who were farming there could no longer live or farm there because of the arid conditions in that whole region and the water supply was now salty.
They migrated up the water ways/rivers entering the Black Sea directly into Europe, taking their farming and their IndoEuropean language with them. Some went into China and are these people, Tocharians.
This flood is also probably the source of Noah's Flood stories. All the oceans of the world were rising, flooding everywhere, because of the end of the Ice Age melt, many islands in the Mediaterranean were submerged, flood refugees were everywhere, the wrath of God had been unleashed...the dam at the Bosporus was broken and the Black Sea Flooded.
Noah saw all this flooding and realized everywhere was going under water so, not knowing how long it would take to flood him out, he began building an arc up on Mt Ararat....it still there somewhere.