Paleolithic
No traces have yet been found in Scotland of either a Neanderthal presence or of Homo sapiens during the Pleistocene interglacials. The first indications of humans occur only after the ice retreated in the 11th millennium BC and the current Flandrian interglacial began. Since that time the landscape of Orkney has been altered by both human and natural forces. Initially, sea levels were lower than at present due to the large volume of ice that remained. This meant that the Orkney islands may have been attached to the mainland, as was the present-day island of Great Britain to Continental Europe. Much of the North Sea basin was also dry land until after 4000 BC. This would have made travel to northern Scotland relatively easy for early human settlers. The subsequent isostatic rise of land makes estimating post-glacial coastlines a complex task.
Read more about this topic: Prehistoric Orkney