The earliest known site of human occupation in Bougainville is Kilu Cave, located on Buka Island. The bottom-most archaeological deposits in the cave were radiocarbon-dated to between 28,700 and 20,100 years ago. During the Last Glacial Maximum, until approximately 10,000 years ago, present-day Bougainville Island was part of a single landmass known as "Greater Bougainville", which spanned from the northern tip of Buka Island to the Nggela Islands north of Guadalcanal. The "obvious immediate origin for its first colonists" of Bougainville is the Bismarck Archipelago to the north, where sites have been identified dating back 35,000 to 40,000 years.