The Solomons were first colonised by people coming from the Bismarck Islands and New Guinea during the Pleistocene era c. 30,000-28,000 BCE, based on archaeological evidence found at Kilu Cave on Buka Island in the Autonomous Region of Bougainville, Papua New Guinea. At this point sea levels were lower and Buka and Bougainville were physically joined to the southern Solomons in one landmass ('Greater Bougainville'), though it is unclear precisely how far south these early settlers spread as no other archaeological sites from this period have been found. As sea levels rose as the Ice Age ended c. 4000-3500 BCE, the Greater Bougainville landmass split into the numerous islands that exist today. Evidence of later human settlements dating to c. 4500-2500 BCE have been found at Poha Cave and Vatuluma Posovi Cave on Guadalcanal. The ethnic identity of these early peoples is unclear, though it is thought that the speakers of the Central Solomon languages (a self-contained language family unrelated to other languages spoken in the Solomons) likely represent the descendants of these earlier settlers.