Canberra is the nation's capital, while its most populous cities are Sydney and Melbourne, each with a population of more than five million. Australia's written history commenced with Dutch exploration of most of the coastline in the 17th century. The ancestors of Aboriginal Australians began arriving from Southeast Asia 50,000 to 65,000 years ago, during the Last Glacial Period. A smaller proportion of Australians are descended from indigenous people, comprising Aboriginal Australians and Torres Strait Islanders. Since the late 1970s, following the end of the White Australia policy in 1973, a large and continuing wave of immigration to Australia from around the world has continued into the 21st century, with Asia now being the largest source of immigrants. Other major international events held regularly in Australia include the Australian Open, one of the four Grand Slam tennis tournaments, and the Formula One Australian Grand Prix. Australia has particularly strong international teams in cricket, field hockey, netball, rugby league, rugby union, and performs well in cycling and swimming. Australia has a long history of visual arts, starting with the cave and bark paintings of its indigenous peoples. The vigor and originality of the arts in Australia—films, opera, music, painting, theater, dance, and crafts—are achieving international recognition. An indigenous language remains the main language for a very small minority of people. Australia has a federal form of government, with a national government for the Commonwealth of Australia and individual state governments (those of New South Wales, Victoria, Queensland, South Australia, Western Australia, and Tasmania). The country’s low relief results from the long and extensive erosive action of the forces of wind, rain, and the heat of the sun during the great periods of geologic time when the continental mass was elevated well above sea level. The American-style concept of a national “frontier” moving outward along a line of settlement is also inappropriate. At least 60,000 years before European explorers sailed into the South Pacific, the first Aboriginal explorers had arrived from Asia, and by 20,000 years ago they had spread throughout the mainland and its chief island outlier, Tasmania. Australia is separated from Indonesia to the northwest by the Timor and Arafura seas, from Papua New Guinea to the northeast by the Coral Sea and the Torres Strait, from the Coral Sea Islands Territory by the Great Barrier Reef, from New Zealand to the southeast by the Tasman Sea, and from Antarctica in the far south by the Indian Ocean. To the south, Australian jurisdiction extends a further 310 miles (500 km) to the southern extremity of the island of Tasmania, and in the north it extends to the southern shores of Papua New Guinea. Australia's population has quadrupled since the end of World War I, spurred by an ambitious immigration program. Most Australians are descended from nineteenth and twentieth-century immigrants from Great Britain and Ireland. Australia's largest export markets include Japan, People's Republic of China, the United States, South Korea, and New Zealand. The service sector, including tourism, education, and financial services, comprises the majority of GDP. All branches of the ADF have been involved in UN and regional peacekeeping, most recently in East Timor, the Solomon Islands, and Sudan, disaster relief, and armed conflict, including the 2003 invasion of Iraq. The most notable exercise of these powers was the dismissal of the Whitlam government in the constitutional crisis of 1975. It is one of the world's oldest federations, in which power is divided between the federal and state governments. The country has maintained its mostly unchanged constitution alongside a stable liberal democratic political system since Federation in 1901. In June 2021, over 1,000 animal and plant species were listed by Australian governments as endangered or critically endangered. Over the past two centuries, Australia has lost more mammal species than any other continent.