The earliest known manifestations of the geologic record of the Australian continent are 4.4-billion-year-old detrital grains of zircon in metasedimentary rocks that were deposited from 3.7 to 3.3 billion years ago. Based on that and other findings, the Precambrian rocks in Australia have been determined to range in age from about 3.7 billion to 541 million years (i.e., to the end of Precambrian time). They are succeeded by rocks of the Paleozoic Era, which extended to about 252 million years ago; of the Mesozoic Era, which lasted until about 66 million years ago; and of the Cenozoic Era, the past 66 million years. For millions of years Australia was part of the supercontinent of Pangaea and subsequently its southern segment, Gondwanaland (or Gondwana). Its separate existence was finally assured by the severing of the last connection between Tasmania and Antarctica, but it has been drifting toward the Southeast Asian landmass. As a continent, Australia thus encompasses two extremes: on the one hand, it contains the oldest known earth material while, on the other, it has stood as a free continent only since about 35 million years ago and is in the process—in terms of geologic time—of merging with Asia, so that its life span as a continent will be of relatively short duration.

Australia is both the flattest continent and, except for Antarctica, the driest. Seen from the air, its vast plains, sometimes the colour of dried blood, more often tawny like a lion’s skin, may seem to be one huge desert. One can fly the roughly 2,000 miles (3,200 km) to Sydney from Darwin in the north or to Sydney from Perth in the west without seeing a town or anything but the most scattered and minute signs of human habitation for vast stretches. A good deal of the central depression and western plateau is indeed desert. Yet appearances can be deceptive. The red and black soil plains of Queensland and New South Wales have long supported the world’s greatest wool industry, and some of the most arid and forbidding areas of Australia conceal great mineral wealth.

Moreover, the coastal rim is, almost everywhere, exempted from the prevailing flatness and aridity. In particular the east coast, where European settlement began and where the majority of Australians now live, is topographically quite diverse and is comparatively well watered and fertile.

Inland from the coast runs a chain of highlands, known as the Great Dividing Range, from Cape York in northern Queensland to the southern seaboard of Tasmania. From the coast that range, which may be anything from 20 miles to 200 miles (30 to 300 km) distant, often appears as a bold range of mountains, though few of its peaks exceed 5,000 feet (1,500 metres). In fact, it is more like the escarpment of a giant plateau, formed of gently rolling hills, which slopes imperceptibly down to the western plains. There are similar, though smaller, stretches of hilly, well-watered land all around the rim of the continent except on the south coast where the Nullarbor Plain stretches to the sea, but everywhere precipitation diminishes rapidly as one penetrates farther from the coast.

In such a huge continent there are wide variations in landforms and climate. The thickly wooded ranges of the Great Divide have little in common with the treeless, sun-baked plains of the Inland. There is a vast difference between the red rocks and monumental hills of central Australia and the tropical rainforests and sugar plantations of northern Queensland. To many visitors, Australia may not seem a pretty country, but it has a unique and haunting beauty that exerts a powerful fascination on those who get to know it.

The Australian Heritage Commission Act of 1975 established a federal agency to develop interest in a National Estate of listed places. Such places would be selected mainly on the basis of aesthetic, historical, scientific, or social significance. The process was not intended to guarantee any area or site against development, but the growing register was, nevertheless, made to serve that purpose on occasion. The UNESCO list of World Heritage sites carries more political and legal weight, and areas so classified have been protected by the federal governments in the face of furious opposition from their state partners. Some 20 Australian landmarks, representing every state and territory, have been added to the list, including the Great Barrier Reef, the Blue Mountains area, Kakadu National Park, Shark Bay, Uluru–Kata Tjuta National Park (which contains the great red mass of Uluru/Ayers Rock, a sacred site of Aboriginal peoples), rainforest reserves in central-eastern Australia, the Tasmanian Wilderness, and fossil mammal sites at Riversleigh and Naracoorte. Territorial disputes have arisen over proposals for the Great Barrier Reef and natural rainforest enclaves in Queensland and Tasmania.

Australia is the arid continent. Over some two-thirds of its landmass, precipitation (largely as rainfall) per annum averages less than 20 inches (500 mm), and over one-third of it is less than 10 inches (250 mm). Little more than one-tenth of the continent receives more than 40 inches (1,000 mm) per year. As has been noted, in winter the snowfields of Tasmania and the Mount Kosciuszko area can be extensive, but on the whole Australia is an extremely hot country, in consequence of which evaporation losses are high and the effectiveness of the rainfall received is reduced. In addition, the severity of climate, the predominance of the outdoors in the minds and lives of many, and the national importance of agricultural and pastoral pursuits all make Australians perhaps more climate-conscious than most. In no country of comparable development do climate and weather loom so large in the lives and conversation of the people.

The principal features of Australia’s climate stem from its position, shape, and size. Australia is mainly a compact tropical and near-tropical continent. No major arms or embayments of the sea penetrate far into the landmass. The only extensive uplands occur near the east coast, and even they are not, by world standards, very high.

In summer (December–February), when the sun is directly overhead in northern Australia, temperatures are extremely high. The sea exerts little moderating influence, and the uplands are not sufficiently extensive or high to have more than local effects. Temperatures commonly soar above the 100 °F (38 °C) mark in the interior, but because there rarely is any cloud cover, radiation loss is considerable at night, and daily temperature ranges are wide. High temperatures dominate the Australian summers in all but Tasmania. Heat waves are common, and, though the highest amounts of solar radiation are received in northern South Australia, the highest temperatures and longest heat waves are recorded in the northwest of Western Australia. For example, Marble Bar has recorded a maximum temperature of 100 °F or more on 162 consecutive days. Temperatures in winter remain moderate except in the uplands of Tasmania and southeastern Australia, where snow is common. Night frosts are common in winter throughout southern Australia and in the interior.

Because of its relatively low latitudinal position, Australia comes under the influence of the southeast trade winds in the north and the westerlies in the south. Northern Australia is affected by a northerly monsoon, partly because of the latitude and the seasonal migration of planetary wind zones and partly because of the summer heating of the continental interior that draws in surface winds. The monsoon brings summer (December–February) rains to the northern coastal area that penetrate inland for variable distances. The summer rains are all the more important because most of northern Australia is in the sheltered rain shadow of the Eastern Uplands, which block the rain-bearing southeast trades in winter. The trades, forced to rise by the uplands, bring heavy rains to the Pacific coasts of Queensland and northern New South Wales. Those areas are also affected by tropical cyclones and receive the heaviest rains of any part of Australia. Within the coastal fringe, the northern Queensland area around Tully, south of Cairns, is the wettest, with an annual average of nearly 160 inches (4,050 mm). Southern Australia receives winter rains from depressions associated with the west-wind zone. Again, there are local topographic controls, with uplands receiving higher amounts than the adjacent plains. Parts of the southern Mount Lofty Range, in South Australia, average more than 40 inches (1,000 mm) of rainfall per year, but Adelaide, to the west, averages only about 20 inches (500 mm), while the Murray plains, in the rain shadows of the range, receive 15 inches (380 mm) or less rainfall annually.

In the great mass of the interior of Australia, annual rainfall averages less than 20 inches (500 mm), and over vast areas the total is less than 10 inches (250 mm); the Lake Eyre region averages less than half that amount. Rainfall in those areas is unreliable and capricious, with long droughts broken by damaging rains and floods. Over Australia as a whole, rainfall is indeed extremely variable. Only in the far north, around Darwin, in the southwest of Western Australia, in southern South Australia and Victoria, in Tasmania, and in eastern New South Wales is the recorded annual precipitation fairly consistent, in any given year totaling no more than 10 percent above or below the long-term average in specific years. Much of Australia’s marked climatic variability has been ascribed to the changeability in differential air pressures over the central Pacific and the Indonesian archipelago, primarily caused by contrasts in sea and ocean temperatures. The resulting large-scale swing in air pressure is known as the Southern Oscillation. Monitoring the Southern Oscillation Index (SOI) is now considered essential to seasonal weather forecasting. The SOI is strongly negative when weak Pacific winds bring less moisture than usual to Australia. Prolonged negative phases are related to El Niño episodes in the South Pacific, and most of Australia’s major droughts have been related to those episodes. Prolonged positive SOI phases (during La Niña) normally bring above-average rainfall and floods to eastern and northern Australia. In each case, however, the correlations are not exact. The Australian climate is also influenced by the phenomenon known as the Indian Ocean Dipole (IOD), which refers to the year to year temperature differences between the eastern and western portions of that body of water. The IOD alternates between three phases—positive, negative, and neutral—each of which generally occurs every three to five years. During the neutral phase, the IOD has little influence on the Australian climate. The increased westerly winds that arise during the negative phase cause warmer water to concentrate northwest of Australia, ultimately producing above-average rainfall in parts of southern Australia. On the other hand, during the positive phase, westerly winds weaken, permitting warmer water to move toward Africa, lessening cloud creation over Australia and reducing rainfall in much of western, southern, and eastern Australia.

The hot, dry weather that is typical for Australia in the summer (December–February) often produces bushfires. In 1939, 71 people we killed in the “Black Friday” blaze in Victoria, and 75 individuals perished in the “Ash Wednesday” fires in Victoria and South Australia in 1983. The scale of the 2009 fires—attributed to extreme weather conditions coupled with a severe and protracted drought that had created tinder-dry vegetation across the state—was unprecedented. The deaths of 173 people that resulted from these “Black Saturday” bushfires left the country in a state of shock. In 2019 prolonged drought and record heat widely attributed to climate change, along with lightning and scattered incidences of arson combined to produce a rash of deadly bushfires that began in September, before the start of the usual fire season, and persisted into the new year. By early January bushfires had occurred in every Australian state, with New South Wales experiencing the worst of it. By the end of the first week in January, 17.9 million acres (7.3 million hectares) had burned throughout Australia, with more than 12 million acres (about 5 million hectares) affected in New South Wales alone. More than two dozen people were killed nationwide.

Today the population of Australia consists of more than 270 ethnic groups. Until the mid-20th century, however, Australian society was, with some accuracy, regarded in the wider world as essentially British—or at any rate Anglo-Celtic. The ties to Britain and Ireland were scarcely affected by immigration from other sources until then. The complex demographic textures in Australia at the beginning of the 21st century contrasted quite sharply with the homogeneity of the country during the first half of the 20th century. Although some nine-tenths of Australia’s population is of European ancestry, more than one-fifth is foreign-born, and there is a small but important (and growing) Aboriginal population. Of those born overseas, about half were born in Europe, though by far the largest proportion of those came from the United Kingdom. Among the larger non-European groups are New Zealanders and Chinese. The growth in immigration, particularly Asian immigration (from China, Vietnam, Hong Kong, and the Philippines) beginning in the last decades of the 20th century, combined with a subsequent flow of refugees from the Balkans, altered the cultural landscape, imbuing Australia with a cosmopolitanism that it lacked in the mid-20th century. Despite the country’s long-standing Anglo-Celtic heritage, two ethnic groups, the Chinese and the Italians, have had an important presence in Australia since the 19th century

Although English is not Australia’s official language, it is effectively the de facto national language and is almost universally spoken. Nevertheless, there are hundreds of Aboriginal languages, though many have become extinct since 1950, and most of the surviving languages have very few speakers. Mabuiag, spoken in the western Torres Strait Islands, and the Western Desert language have about 8,000 and 4,000 speakers, respectively, and about 50,000 Aboriginal people may still have some knowledge of an Australian language. (For full discussion, see Australian Aboriginal languages.) The languages of immigrant groups in Australia are also spoken, most notably Chinese, Italian, and Greek.

Recorded religious adherence has generally mirrored the immigrants’ backgrounds. In every census since the early colonial era, most Australians have professed to be Christian, principally Anglican and Roman Catholic, but simple materialism has become more influential than Christianity. The number of Roman Catholics exceeded the number of Anglicans for the first time in the late 1980s. In the early 21st century more than one-half of Australians identified themselves as Christian; about one-fourth were Roman Catholic and one-fifth Anglican. Smaller proportions belonged to other Protestant denominations (notably Uniting Church, Presbyterian, and Reformed), and there were also small groups of Jews and Hindus. The proportions registering as Orthodox Christians, Muslims, and Buddhists increased sharply in the late 20th century. Almost one-fourth of Australians professed no religion. In contrast to the European settlers, traditional Aboriginal communities are intensely spiritual. There religion gives meaning to life, and the coordinating theme is the sustaining connection between land and people.

Australia is a land like no other, with about one million different native species. More than 80 per cent of the country’s flowering plants, mammals, reptiles and frogs are unique to Australia, along with most of its freshwater fish and almost half of its birds. Australia’s marine environment is home to 4000 fish species, 1700 coral species, 50 types of marine mammal and a wide range of seabirds. Most marine species found in southern Australian waters occur nowhere else. Australia’s geographic isolation has meant that much of its flora and fauna is very different from species in other parts of the world. Most are found nowhere else. However, some closely related species are found on the continents which once made up the ancient southern supercontinent Gondwana. Covered in rainforest and ferns 300 million years ago, Gondwana included South America, Africa, India and Antarctica. Most of Australia’s flora and fauna have their origins in Gondwana, which broke up about 140 million years ago. Australia separated from Antarctica 50 million years ago. As it drifted away from the southern polar region, its climate became warmer and drier and new species of plants and animals evolved and came to dominate the landscape.

Flora

Most of the Gondwanan forests were replaced by tough-leaved open forests of eucalypts and acacias. Some isolated remnants of the ancient Gondwanan forests remain. These include the cool and warm temperate rainforests of Tasmania and eastern Australia and the dry rainforests or scrub forests of northern Australia. These forests have high conservation values.


In 1994, the Wollemi Pine was found in a remote valley in the Blue Mountains of New South Wales. It is believed to be representative of a now extinct group of trees that existed at the time of the dinosaurs, making it a species that has been around for 65 million years. There are now an estimated 20 000 vascular and 7700 non-vascular plants, and 250 000 species of fungi in Australia. Plants include living fossils such as the cycad palm and the grass tree, and brilliant wildflowers such as the waratah, Sturt’s desert pea, banksia and kangaroo paws. Australia has over 1000 species of acacia, which Australians call ‘wattle’, and around 2800 species in the Myrtaceaefamily, which includes eucalypts (or gum trees) and melaleucas.


Wildflowers, including everlasting daisies, turn the arid and savanna grassland areas of Australia into carpets of colour after rain. Native forests are limited to wetter coastal districts, and rainforests are found mainly in Queensland.


The high diversity of flora includes large numbers of species in ecologically significant genera such as Acacia,Eucalyptus, Melaleuca, Grevillea and Allocasuarina. Acacias tend to dominate in drier inland parts of Australia, while eucalypts dominate in wetter parts. Australia’s unique flora includes the Proteaceae family of Banksia, Dryandra,Grevillea, Hakea and Telopea (waratah).


The most common vegetation types today are those that have adapted to arid conditions, where the land has not been cleared for agriculture. The dominant type of vegetation in Australia—23 per cent—is the hummock grasslands in Western Australia, South Australia and the Northern Territory. In the east eucalypt woodlands are prevalent, and in the west there are Acacia forests, woodlands and shrublands. Tussock grasslands are found largely in Queensland.

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Fauna

In Australia there are more than 378 species of mammals, 828 species of birds, 300 species of lizards, 140 species of snakes and two species of crocodiles. Of the mammals, almost half are marsupials. The rest are either placental mammals or monotremes. Among Australia’s best-known animals are the kangaroo, koala, echidna, dingo, platypus, wallaby and wombat. Australia has more than 140 species of marsupials, including kangaroos, wallabies, koalas, wombats and the Tasmanian Devil, which is now found only in Tasmania. There are 55 different species of kangaroos and wallabies—macropods—native to Australia. Macropods vary greatly in size and weight, ranging from half a kilogram to 90 kilograms. The main difference between wallabies and kangaroos is in size— wallabies tend to be smaller. Some stand as tall as humans and others are as small as domestic cats.


In many rural areas where their populations are high, kangaroos are regarded as pests because they compete with sheep and cattle for scarce pasture and water. Kangaroo harvesting contributes to the sustainability of the Australian environment. Estimates of Australia’s kangaroo population vary between 30 and 60 million. The dingo is Australia’s native wild dog and its largest carnivorous mammal. In some pastoral areas, dingoes are also regarded as pests due to the threat they pose to sheep and other farm animals. In an effort to keep fertile south-east Australia relatively free of dingoes, the world’s largest fence was built, spanning 5320 kilometres from Queensland to South Australia. Australia hosts another unique animal group, the monotremes, which are egg-laying mammals, often referred to as ‘living fossils’. The most distinctive is the platypus, a riverdwelling animal with a duck-like bill, a furry body and webbed feet.


Of the 828 bird species listed in Australia, about half are found nowhere else. Isolation has also contributed to the development and survival of unusual birds. These range from tiny honeyeaters to the large, flightless emu, which stands nearly two metres tall. In between is a vast array of waterbirds, seabirds and birds that dwell in open woodlands and forests. Some outstanding examples are cassowaries, black swans, fairy penguins, kookaburras, lyrebirds and currawongs. There are 55 species of parrots in Australia. Many of these birds are as numerous as they are colourful, including a spectacular variety of cockatoos, rosellas, lorikeets, cockatiels, parakeets and budgerigars.


Australia has more species of venomous snakes than any other continent (21 of the world’s 25 deadliest snakes). Fear of snake bites is common among people planning to travel in Australia. However, bites are rare and most often occur when a snake is deliberately provoked by a human.


Australia’s diverse oceans support around 4000 of the world’s 22 000 types of fish, as well as 30 of the world’s 58 seagrass species. Australia is also home to the world’s largest coral reef system, the UNESCO World Heritage-listed Great Barrier Reef. Marine species of note include the predatory great white shark, which grows up to six metres in length; the giant filter-feeding whale shark, which can reach lengths of 12 metres; the bluebottle or Portuguese man-of-war, which is a common hazard at many Australian beaches; and the box jellyfish, which is one of the most venomous animals in the world.

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