The degree to which Aboriginal and Torres Strait Islander people on the Australian continent practised agriculture has long been debated by archaeologists. Earlier it was believed that Australian Aboriginal people were ignorant of the principles of agriculture, but this has since been disproven. For instance, Australian Aboriginal women in traditional societies often transplanted immature "bush tucker" plants found growing in unfavourable locations to more favourable spots. There were also a number of plants (particularly seeds and roots) that could have lent themselves to cultivation, and were used in making such foods as damper. Charles Sturt in his 1844 expedition to northwest New South Wales and central Australia reports seeing large haystacks built by Aboriginal people of seed crops. This was located east of Depot Glen Milparinka about 600 km from the Murray River. Firestick farming has also always been a technique used by Aboriginal people to open the canopy of closed canopy forests, introducing sunlight to the ground, and prompting germination of a number of foodstuffs known to attract kangaroo and other marsupials. This would encourage a more intensive land use than otherwise. But the main reason for the lack of agriculture in Australia is the extreme variability of the climate. Australia is the only continent on Earth, which, as a result of the El Nino Southern Oscillation, experiences greater variability between years than it does between the seasons. Such climatic variability makes farming very difficult, especially for incipient farmers who cannot be supported from outside their community. Australian Aboriginal people found that maintaining stable populations below the effective carrying capacity of the environment would enable an adequate supply of food, even in drought years, so maintaining a stable culture. This made hunting and gathering a more sustainable activity on the Australian continent than neolithic farming. Evidence of cultivation at Kuk in Papua New Guinea, from about 10–12,000 years BP (at a time when that island was joined to Australia, suggests crop raising was possible in the Sahul supercontinent when conditions were favourable.