The Ural Mountains extend from the Arctic Ocean in the north to the Ural River and northwestern Kazakhstan in the south over a distance of 1,500 mi (2,400 km), the boundary between Europe and Asia. Human occupation begins in the Paleolithic and continues to this day. Earliest presence is documented for the Homo neanderthalensis. Although no Neanderthal fossils were ever discovered, stone tools found at Byzovaya, that date to 33,000 years ago are attributed to the Mousterian culture.