major component of national tourism incomes. Tourism Australia explicitly markets nature-based and Indigenous-led experiences to tourists. In the 2015–2016 financial year, 815,000 visitors spent $988 million while on holidays in the Northern Territory alone. There are many popular tourist attractions in the Outback. Some of the well known destinations include Devils Marbles, Kakadu National Park, Kata Tjuta (The Olgas), MacDonnell Ranges and Uluru (Ayers Rock). Mining Other than agriculture and tourism, the main economic activity in this vast and sparsely settled area is mining. Owing to the almost complete absence of mountain building and glaciation since the Permian (in many areas since the Cambrian) ages, the outback is extremely rich in iron, aluminium, manganese and uranium ores, and also contains major deposits of gold, nickel, copper, lead and zinc ores. Because of its size, the value of grazing and mining is considerable. Major mines and mining areas in the Outback include opals at Coober Pedy, Lightning Ridge and White Cliffs, metals at Broken Hill, Tennant Creek, Olympic Dam and the remote Challenger Mine. Oil and gas are extracted in the Cooper Basin around Moomba. In Western Australia the Argyle diamond mine in the Kimberley is the world's biggest producer of natural diamonds and contributes approximately one-third of the world's natural supply. The Pilbara region's economy is dominated by mining and petroleum industries. Most of Australia's iron ore is also mined in the Pilbara and it also has one of the world's major manganese mines. Population Aboriginal communities in outback regions, such as the Anangu Pitjantjatjara Yankunytjatjara lands in northern South Australia, have not been displaced as they have been in areas of intensive agriculture and large cities, in coastal areas. The total population of the Outback in Australia declined from 700,000 in 1996 to 690,000 in 2006. The largest decline was in the Outback Northern Territory, while the Kimberley and Pilbara showed population increases during the same period. The sex ratio is 1040 males for 1000 females and 17% of the total population is indigenous. Facilities The Royal Flying Doctor Service (RFDS) started service in 1928 and helps people who live in the outback of Australia. Previously, serious injuries or illnesses often meant death owing to the lack of proper medical facilities and trained personnel. In many outback communities, the number of children is too small for a conventional school to operate. Children are educated at home by the School