Australia, island continent located southeast of Asia and forming, with the nearby island of Tasmania, the Commonwealth of Australia, a self-governing member of the Commonwealth of Nations. The continent is bounded on the north by the Timor Sea, the Arafura Sea, and the Torres Strait; on the east by the Coral Sea and the Tasman Sea; on the south by the Bass Strait and the Indian Ocean; and on the west by the Indian Ocean. The commonwealth extends about 4,000 km (about 2,500 mi) from east to west and about 3,700 km (about 2,300 mi) from north to south. The area of the commonwealth is 7,682,300 sq km (2,966,200 sq mi), and the area of the continent alone is 7,614,500 sq km (2,939,974 sq mi), making Australia the smallest continent in the world, but the sixth largest country. The capital of Australia is Canberra, and the largest city is Sydney; both are located in the southeast.

The Commonwealth of Australia is made up of six states—New South Wales, Queensland, South Australia, Tasmania, Victoria, and Western Australia—and two territories—the Australian Capital Territory and the Northern Territory. The external dependencies of Australia are the Territory of Ashmore and Cartier Islands, the Australian Antarctic Territory, Christmas Island, the Territory of Cocos Islands (also called the Keeling Islands), the Coral Sea Islands Territory, the Territory of Heard Island and McDonald Islands, and Norfolk Island.

The first inhabitants of Australia were the Aboriginal people, who migrated to the continent some 50,000 to 60,000 years ago. The continent remained relatively unknown to most of the outside world until the 17th century. The first permanent European settlement was established in 1788 at Port Jackson, in southeastern Australia, as a British penal colony; it grew into the city of Sydney. Australia developed as a group of British colonies during the 19th century, and in 1901 the colonies federated to form a unified independent nation, the Commonwealth of Australia.

Australia lacks mountains of great height; it is one of the world’s flattest landmasses. The average elevation is about 300 m (about 1,000 ft). The interior, referred to as the outback, is predominantly a series of great plains, or low plateaus, which are generally higher in the northeast. Low-lying coastal plains, averaging about 65 km (about 40 mi) in width, fringe the continent. In the east, southeast, and southwest, these plains are the most densely populated areas of Australia.

In the east the coastal plains are separated from the vast interior plains by the Great Dividing Range, or Eastern Highlands. This mountainous region averages about 1,200 m (about 4,000 ft) in height and stretches along the eastern coast from Cape York in the north to Victoria in the southeast. Much of the region consists of high plateaus broken by gorges and canyons. Subdivisions of the range bear many local names, including, from north to south, the New England Plateau, Blue Mountains, and Australian Alps; in Victoria, where the range extends westward, it is known as the Grampian Mountains, or by its Aboriginal name, Gariwerd. The highest peak in the Australian Alps, and the highest in Australia, is Mount Kosciusko (2,228 m/7,310 ft), in New South Wales.

A section of the Great Dividing Range is in Tasmania, which is located about 240 km (about 150 mi) from the southeastern tip of the continent and is separated from it by Bass Strait. The waters of the strait are shallow, with an average depth of 70 m (230 ft). The major islands in the strait are the Furneaux Group and Kent Group in the east, and King, Hunter, Three Hummock, and Robbins islands in the west.

The western half of the continent is an enormous plateau, about 300 to 450 m (about 1,000 to 1,500 ft) above sea level. The Great Western Plateau includes the Great Sandy, Great Victoria, and Gibson deserts. Western Australia has, in its northern half, several isolated mountain ranges, including the King Leopold and Hamersley ranges. The interior is relatively flat except for several eroded mountain chains, such as the Stuart Range and the Musgrave Ranges in the northern part of South Australia and the Macdonnell Ranges in the southern part of the Northern Territory.

The central basin, or the Central-Eastern Lowlands, is an area of vast, rolling plains that extends west from the Great Dividing Range to the Great Western Plateau. In this region lies the richest pastoral and agricultural land in Australia. Uluru (Ayers Rock), in the center of Australia in Uluru-Kata Tjuta National Park, is one of the largest monoliths in the world. It is 9 km (6 mi) around its base and rises sharply to some 348 m (1,142 ft) above the surrounding flat, arid land. Other mountain ranges of limited size in the central part of Australia are the Flinders Ranges and Mount Lofty Ranges in South Australia. The area along the south central coast is called the Nullarbor Plain. The Nullarbor is a vast, arid, limestone plateau that is virtually uninhabited. It has an extensive system of caverns, tunnels, and sinkholes that contain valuable geological information about life in ancient Australia. Extinct volcanic craters are located in the southeastern part of South Australia and in Victoria.

The coastline of Australia measures some 25,760 km (16,010 mi). It is generally regular, with few bays or capes. The largest inlets are the Gulf of Carpentaria in the north and the Great Australian Bight in the south. The several fine harbors include those of Sydney, Hobart, Port Lincoln, and Albany.

The Great Barrier Reef is the largest known coral formation in the world. It extends some 2,010 km (some 1,250 mi) along the eastern coast of Queensland from Cape York in the north to Bundaberg in the south. The chain of reefs forms a natural breakwater along the coast for vessels of modest size but is sometimes hazardous for larger ships.

Australia was once part of the enormous landmass Gondwanaland, which earlier formed part of the supercontinent Pangaea. Much of its geological history is remarkably ancient; the oldest known rock formations date from 3 billion to 4.3 billion years ago.

The great plateau of western Australia is underlain by a vast, stable shield of Precambrian metamorphic and igneous rocks, ranging in age from 570 million to 3 billion years old. These form the core of the ancestral continent, which, with Antarctica, had split off from Gondwanaland during the Jurassic Period, less than 200 million years ago, and had begun drifting eastward (see Plate Tectonics). Australia began to assume its modern configuration by the Eocene Epoch, some 50 million years ago, when Antarctica broke away and drifted southward.

The thick sedimentary rocks of the Great Dividing Range were deposited in a long, broad north-south depression, or geosyncline, during an interval that spanned most of the Paleozoic Era (570 million to 225 million years ago). Compressive forces buckled these rocks at least twice during the era, forming mountain ranges and chains of volcanoes. However, the volcanoes have long since become extinct, and as a result the mountain ranges are extremely eroded.

The Great Dividing Range separates rivers that flow east to the coast from those that flow westerly across the plains through the interior. The most important of the rivers that flow toward the eastern coast are the Burdekin, Fitzroy, Hunter, and Nepean-Hawkesbury. The Fitzroy River forms a large drainage basin in Queensland. The Murray-Darling-Murrumbidgee network, which flows inland from the Great Dividing Range, drains an area of more than 1 million sq km (400,000 sq mi) in Queensland, New South Wales, Victoria, and South Australia. The Murray River and its main tributary, the Darling, total about 5,300 km (about 3,300 mi) in length. The Murray River itself forms most of the border between New South Wales and Victoria. Considerable lengths of the Murray, Darling, and Murrumbidgee rivers are navigable during the wet seasons.

The central plains region, also known as the Channel Country, is interlaced by a network of rivers. During the rainy season these rivers flood the low-lying countryside, but in dry months they become merely a series of water holes. The Victoria, Daly, and Roper rivers drain a section of the Northern Territory. In Queensland the main rivers flowing north to the Gulf of Carpentaria are the Mitchell, Flinders, Gilbert, and Leichhardt. Western Australia has few major rivers. The most important are the Fitzroy (different from the Fitzroy in Queensland), Ashburton, Gascoyne, Murchison, and Swan rivers.

Because of Australia’s scarce water resources, dams have been constructed on some rivers to supply cities with water and to support irrigation farming. The Snowy Mountains Scheme (1949-1972) and the Ord River Scheme (1960-1972) are the two largest water-conservation projects. The Snowy Mountains Scheme, in the southeastern highlands in New South Wales, is an enormous, multipurpose engineering project that was financed by the federal and state governments to supply water for irrigation, domestic and livestock use, and for the generation of hydroelectricity. The Ord River Scheme is an irrigation project in the remote Kimberley region of Western Australia. During its construction the scheme attracted criticism from economists, ecologists, environmentalists, and agricultural scientists. Today the long-term environmental and economic viability of the scheme remains in question, while only a small fraction of the arable land that could receive irrigation water is being cultivated due to destructive crop pests and poor soil quality.

Most of the major natural lakes of Australia contain salt water. The great network of salt lakes in South Australia—Lake Eyre, Lake Torrens, Lake Frome, and Lake Gairdner—is the remains of a vast inland sea that once extended south from the Gulf of Carpentaria. During the dry season many of the salt lakes become salt-encrusted swamp beds or clay pans. Lake Argyle, created by the construction of the Ord River Scheme, is one of Australia’s largest artificially created freshwater lakes.

Large areas of the interior, which otherwise would be useless for agriculture, contain water reserves beneath the surface of the land. These artesian water reserves, usually found at a great depth, are tapped by drilling to provide water essential for livestock. Artesian water reserves underlie about 2.5 million sq km (about 1 million sq mi) of Australia. The Great Artesian Basin, extending from the Gulf of Carpentaria into the northern part of New South Wales, covers more than 1.7 million sq km (700,000 sq mi). Other artesian basins are in the northwest, southeast, and along the Great Australian Bight.

The climate of Australia varies greatly from region to region, with a tropical climate in the north, an arid or semiarid climate in much of the interior, and a temperate climate in the south. Despite these variations, the moderating influence of the surrounding oceans and the absence of extensive high mountain ranges help prevent marked extremes of weather. However, some areas occasionally experience extreme weather conditions, such as tropical cyclones, tornadoes, and severe drought.

Because Australia is in the Southern Hemisphere, its seasons are the reverse of those in the Northern Hemisphere. Seasonal variations, on the whole, are small. Generally, coastal and highland areas, especially in the southeast, are cooler than interior locations, and the north, particularly the northwestern coast, is the hottest region. The temperate regions of southern Australia have four seasons, with cool winters and warm summers. January and February are the warmest months, with average temperatures of between 18° and 21°C (65° and 70°F). June and July are the coldest months, with an average July temperature of about 10°C (about 50°F), except in the Australian Alps, where temperatures average 2°C (35°F). In Alice Springs, one of the few population centers in the vast arid interior of the continent, January temperatures average a daily high of 36°C (97°F), and July temperatures average a daily high of 19°C (66°F). Seasonal variations are much less pronounced in northern Australia, which has a tropical climate. This region essentially has only two seasons: a hot, wet period with heavy rainfall mainly in February and March, when the northwestern monsoons prevail; and a warm, dry interval characterized by the prevalence of southeasterly winds. In Darwin, on the northern coast, January temperatures average a daily high of 32°C (90°F), and July temperatures average a daily high of 30°C (86°F).

Australia is the driest of the inhabited continents. The arid and semiarid deserts and plains of central and western Australia encompass more than two-thirds of the continent’s area. The deserts have an annual rainfall of less than 250 mm (10 in). In most years, extensive portions of the continent experience drought conditions. However, annual rainfall is much greater in the coastal regions of northern, eastern, and southern Australia. The northern coast of Australia has a tropical monsoonal climate. Many points on the northern and northeastern coast have average annual rainfall of 1,500 mm (60 in); in some areas of the northwestern coast in Queensland, average annual rainfall exceeds 2,500 mm (100 in). Between December and April the northern coastal regions are subject to tropical cyclones, which bring high winds and torrential rains that can be destructive.

The eastern coastal lowlands receive rain in all seasons, although mostly in summer. The warm, temperate western and southern coasts receive rain mainly in the winter months, usually from prevailing westerly winds. Tasmania, lying in the cool temperate zone, receives heavy rainfall from the prevailing westerly winds in summer and from cyclonic storms in winter. Over the greater part of the lowlands, snow is unknown; however, in the mountains, particularly the Australian Alps in southern New South Wales and the northern part of Victoria, snowfall is occasionally heavy.

All of the southern states are exposed to hot, dry winds from the interior, which can suddenly raise the temperature considerably. Southeastern Australia, including Tasmania, has among the highest incidences of serious bushfires in the world, along with California in the United States and Mediterranean Europe. In 1994, notably, bushfires swept through New South Wales and destroyed several hundred homes in suburban Sydney.

Australia is rich in mineral resources, notably bauxite, coal, diamonds, gold, iron ore, mineral sands, natural gas, nickel, petroleum, and uranium. Readily cultivable farmland is at a premium because much of the land is desert. Australia, however, has become one of the leading agricultural producers in the world by applying modern irrigation techniques to vast tracts of arid soil.

The plant and animal life of Australia is biologically diverse and distinctive. Many of the native plant and animal species are endemic, meaning they do not naturally occur elsewhere. They developed only on the Australian continent because it was isolated from the wider world for more than 50 million years. In addition to its native species, Australia is home to many other plants and animals that humans introduced, mostly since the late 18th century. Many of the introduced species, such as European rabbits and the American prickly pear cactus, invade the habitats of native species and threaten their survival, as well as the delicate balance of the natural ecosystem.

Australia’s dominant natural vegetation is essentially evergreen, ranging from the dense bushland and eucalyptus forests of the coast, to the mulga and mallee scrub and saltbush of the inland plains. The tropical northeastern belt, with its abundant seasonal rainfall and high temperatures, is heavily forested. Palms, ferns, and vines grow prolifically among the oaks, ash, cedar, brush box, and beeches. Mangroves line the mud flats and inlets of the low-lying northern coastline. The crimson waratah, golden-red banksias, and scarlet firewheel tree add color to northern forests.

Along the eastern coast and into Tasmania are pine forests. Pine ranks second to the eucalyptus in terms of economic importance. The Huon and King William pines are particularly valuable for their timber, but the Huon pine is now considered rare and is usually protected. In the forest regions of the warm, well-watered southeastern and southwestern sectors, eucalyptus predominates; more than 500 species are found, some reaching a height of 90 m (300 ft). The mountain ash, blue gums, and woolly butts of the southeast mingle with undergrowth of wattles and tree ferns.

The jarrah and karri species of eucalyptus, which yield timber valued for hardness and durability, and several species of grass tree are unique to Western Australia. The wildflowers of the region are varied and spectacular. In the less dense regions of the interior slopes grow red and green kangaroo paws, scented boronia, waxflowers, bottle brushes, and smaller eucalyptuses, such as the stringybark, red gum, and ironbark. More than 500 species of acacia are indigenous to Australia. The scented flower of one acacia, the golden wattle, is the national flower of Australia and appears on the official coat of arms. In the interior region, where rainfall is low and erratic, characteristic plants are saltbush and spinifex grass, which provide fodder for sheep, and mallee and mulga shrubs.

The most valuable native grasses for fodder, including flinders grass, are found in Queensland and northern New South Wales. During occasional seasonal floods, native grasses and desert wildflowers grow rapidly and luxuriantly, and water lilies dot the streams and lagoons.

The survival of more than 1,000 native plant species is considered threatened. Activities such as commercial agriculture, livestock grazing, and forestry have significantly altered or removed nearly all of the native vegetation in many areas of the continent. Fast-spreading introduced plants such as weeds and ornamentals pose an exceptional menace to native vegetation. The mimosa plant, capable of growing more than 6 m (20 ft) and doubling in area each year, has become a prime threat to the Kakadu World Heritage Area in the Northern Territory. Other widespread nonnative plants include blackberry and gorse from Europe; bridal creeper from South Africa; rubber vine from Madagascar; and paloverde, lantana, and mesquite from Central America. Most of these imports were associated with developments in commercial agriculture or were used as garden ornamentals; about 30 percent have been classified as “garden escapees.” The uncontrolled spread of these plants has caused financial losses in the billions of dollars.

A large proportion of Australia’s native animal species exist nowhere else in the world. Of Australia’s animal species, it is estimated that 84 percent of mammals, 89 percent of reptiles, 93 percent of frogs, and 45 percent of birds are endemic. Some archaic species, such as the Queensland lungfish, have changed little since Paleozoic or Mesozoic times. Scientists estimate that 19 land mammals and 20 birds have become extinct (that is, not sighted in the wild for at least 50 years) since European settlement. The World Conservation Monitoring Centre classifies 63 mammals, 37 birds, 38 reptiles, and 35 amphibians as threatened.

One striking aspect of the native mammal life in Australia is the absence of representatives of most of the orders found on other continents. In contrast to other continents, Australia has a preponderance of marsupials (mammals that raise their young in a marsupium, or abdominal pouch), with some 144 original species (10 became extinct after 1788). Australia is also noted for its comparatively abundant presence of monotremes, which are egg-laying mammals. Only two types of monotremes native to Australia are known to survive. The platypus, a zoological curiosity, is a semiaquatic, furred mammal with an elongated snout resembling a duck bill; the legs of the adult male platypus are equipped with poisonous bony spurs for defense. The platypus is found in eastern and southern Australia, including Tasmania. The other monotreme is the spiny anteater, or echidna, which is found throughout Australia as well as New Guinea.

The best-known marsupials of Australia are the kangaroos, which include about 50 species. Kangaroos are herbivores. They dwell in many areas of the country, and some have become so accustomed to humans they can be considered tame. The large red or gray kangaroo may stand as high as 2 m (7 ft) and can leap up to 9 m (30 ft). The wallaby and kangaroo rat are smaller members of the kangaroo family. The phalangers are herbivorous marsupials that live in trees, including the ringtail possum. The koala, also a tree-dwelling marsupial, is found in the wild only in the eucalyptus forests of eastern Australia. Other well-known marsupials are the burrowing wombat, bandicoot, and pouched mouse. The carnivorous Tasmanian devil, principally a scavenger, is found only on the island of Tasmania.

Rodents, bats, and the dingo belong to a different order of mammals. Scientists believe they were the earliest significant nonnative species, arriving from the Asian mainland and the string of islands to the north of Australia thousands of years ago. While rodents and bats migrated on their own, the doglike dingo was perhaps the first species to be introduced by humans. It is believed that dingoes were introduced into Australia about 4,000 years ago by seafarers from Southeast Asia and the Indonesian islands.

When Europeans settled in Australia, they brought many species of animals with them. Many of these originally domesticated animals have established large feral (wild) populations, including horses (locally known as brumbies), cattle, cats, camels, deer, dogs, donkeys, goats, pigs, rabbits, and water buffalo. These animals have spread throughout the country, most notably in the sparsely populated outback, causing serious ecological and economic damage. The most widespread damage has been caused by the European rabbit, which was brought to Australia in the mid-19th century mainly for sport. These rabbits quickly reached plague proportions on the continent, where they had no natural predators, and their total population reached as many as 500 million. The damage they cause includes soil erosion, the destruction of habitat for native species, and large agricultural losses. Rabbits, as well as foxes and feral cats, have been repeatedly targeted for massive national efforts in biological control and regional eradication programs.

Another introduced species, the South American cane toad, was imported in 1935 from Hawaii into Queensland’s sugarcane country in the hope of controlling beetles and other insect pests. However, it became a grotesquely successful pest in its own right. In the absence of serious predators, the toad has infested much of the state and is migrating into the northern tropics.

Australia’s indigenous amphibians are modest in number due to the prevailingly dry climate. However, some have developed ways to survive the harsh climate of the Australian outback. The burrowing bullfrog, for example, emerges from its underground home to feed and mate only during the brief, infrequent rains.

Australia contains a wide variety of reptile life. In fact, a majority of the land vertebrates are in this class. There are more than 500 species of lizards, including the gecko, skink, and the giant goanna. About 100 species of venomous snakes are found in Australia. The taipan of the far north, the death adder, the tiger snake of the south, the copperhead, and the black snake are the best known of the poisonous snakes. Australia also has two species of freshwater crocodiles. The larger of these, found in the estuaries and coastal swamps along the northern coast, attains lengths of 6 m (20 ft).

The waters surrounding Australia support a wide variety of fish and aquatic mammals. Several species of whales populate southern waters, and seals inhabit parts of the southern coast, the islands in Bass Strait, and Tasmania. Dugong, trepang (sea cucumber), trochus, and pearl shell are found in northern waters. Edible fish and shellfish are abundant, and the oyster, abalone, and crayfish of the warmer southern waters have been exploited commercially. Australian waters contain some 70 species of shark, several of which are dangerous to humans. The Queensland lungfish, sometimes called a living fossil, breathes with its single lung when low river levels render its gills ineffective. Australia has about 3,000 species of marine and freshwater fish. Introduced species, most conspicuously the European carp, threaten the survival of many native species.

Most insect types are represented in Australia, including flies, beetles, butterflies, bees, mosquitoes, and ants. Several of the 260 or so types of mosquitoes are responsible for the transmission of disease to animals and humans in the country’s tropical and temperate regions. The giant termites of northern Australia build huge, hill-like nests up to 6 m (20 ft) in height. Australia has earthworms in abundance, including the giant earthworms of Victoria, which range from 0.9 to 3.7 m (3 to 12 ft) in length, reportedly the longest in the world.

Australia is the home of 649 known species of birds, ranging from archaic types, such as the giant, flightless emu and cassowary, to highly developed species. The fan-tailed lyrebird has great powers of mimicry. The male bowerbirds build intricate and decorative playgrounds to attract females. The largest species of kookaburra has a raucous call for which it is nicknamed the “laughing jackass.” Many varieties of cockatoos and parrots are found; the budgerigar is a favorite of bird fanciers. The white cockatoo, a clever mimic, is more common than the black cockatoo. Black swans, spoonbills, herons, and ducks frequent inland waters. Smaller birds include wrens, finches, titmice, larks, and swallows. Gulls, terns, gannets, mutton birds, albatrosses, and penguins are the most common seabirds. The mutton bird, found mainly on the islands of Bass Strait, is valued for its edible flesh.

All major soil types are present to varying degrees throughout the continent. The arid and semiarid regions provide the most extensive group of soils. These soils are mainly suitable only for light lives