Aboriginal Australian culture is one of the oldest continuous cultures on Earth.[30][69][70][71] At the time of first European contact, Aboriginal Australians were complex hunter-gatherers with diverse economies and societies, and spread across at least 250 different language groups.[72][73] Estimates of the Aboriginal population before British settlement range from 300,000 to one million.[74][75] Aboriginal Australians have an oral culture with spiritual values based on reverence for the land and a belief in the Dreamtime.[76] Certain groups engaged in fire-stick farming,[77][78] fish farming,[79][80] and built semi-permanent shelters.[81][82] The extent to which some groups engaged in agriculture is controversial.[83][84][85]