The Australian landmass, reaching northwards to Papua New Guinea and including Tasmania in the south, was inhabited in prehistoric times until adverse climatic conditions led to an exodus between 15,000 and 25,000 years ago. Stone tools date to 2000–1000 BC. The Aboriginal society was based on extended family groups. At maximum there were 1m. Aborigines, using 200 different languages. By the early 18th century contact was made with traders from the area of modern Indonesia and Papua New Guinea.