When sea levels were lower during the Pleistocene ice age, including the Last Glacial Maximum about 18,000 BC, they were connected by dry land into the combined landmass of Sahul.

During the past 18,000 to 10,000 years, rising sea levels overflowed the lowlands and separated the continent into today's low-lying arid to semi-arid mainland and the two mountainous islands of New Guinea and Tasmania.

These divisions [are] generally themselves spoken as continents, and to them has been added another, embracing the large island of Australia and numerous others in the [Pacific] Ocean, under the name of Oceania.

"[22] The American author Samuel Griswold Goodrich wrote in his 1854 book History of All Nations that, "geographers have agreed to consider the island world of the Pacific Ocean as a third continent, under the name Oceania."

[23] In his 1879 book Australasia, British naturalist Alfred Russel Wallace commented that, "Oceania is the word often used by continental geographers to describe the great world of islands we are now entering upon" and that "Australia forms its central and most important feature.

In the 19th century, many geographers divided up Oceania into mostly racially-based subdivisions; Australasia, Malaysia (encompassing Malay Archipelago), Melanesia, Micronesia and Polynesia.

[25] Today, the Malay Archipelago is typically considered part of Southeast Asia, and the term Oceania is often used to denote the region encompassing the Australian continent, Zealandia, and various islands in the Pacific Ocean that are not included in the seven-continent model.

[29] The island states of Indonesia, Japan, the Philippines, Singapore and Taiwan, all located within the bounds of the Pacific or associated marginal seas, are excluded from the UN definition.

In countries such as Argentina, Brazil, China, Chile, Costa Rica, Ecuador, France, Greece, Italy, Mexico, the Netherlands, Peru, Spain, Switzerland or Venezuela, Oceania is treated as a continent in the sense that it is "one of the parts of the world", and Australia is only seen as an island nation.

In other countries, including Kazakhstan, Poland and Russia, Australia and Eurasia are thought of as continents, while Asia, Europe and Oceania are regarded as "parts of the world".

Before the 1970s, the single Pleistocene landmass was called Australasia, derived from the Latin australis, meaning "southern", although this word is most often used for a wider region that includes lands like New Zealand that are not on the same continental shelf.

During the past 18,000[46] to 10,000 years, rising sea levels overflowed the lowlands and separated the continent into today's low-lying arid to semi-arid mainland and the two mountainous islands of New Guinea and Tasmania.

[51] The lands were joined with Antarctica as part of the southern supercontinent Gondwana until the plate began to drift north about 96 million years ago.

A northern arc consisting of the New Guinea Highlands, the Raja Ampat Islands, and Halmahera was uplifted by the northward migration of Australia and subduction of the Pacific Plate.

There is evidence of genetic and linguistic interchange between Australians in the far north and the Austronesian peoples of modern-day New Guinea and the islands, but this may be the result of recent trade and intermarriage.

[67] Recent archaeological research suggests that 50,000 years ago people may have occupied sites in the highlands at New Guinean altitudes of up to 2,000 m (6,600 ft), rather than being restricted to warmer coastal areas.

[68] Legends of Terra Australis Incognita—an "unknown land of the South"—date back to Roman times and before, and were commonplace in medieval geography, although not based on any documented knowledge of the continent.

At its largest, the continent included Tierra del Fuego, separated from South America by a small strait; New Guinea; and what would come to be called Australia.

[75] In 1606, Dutch navigator Willem Janszoon made the first documented European sight and landing on the continent of Australia in Cape York Peninsula.

When Europeans first arrived, inhabitants of New Guinea and nearby islands, whose technologies included bone, wood, and stone tools, had a productive agricultural system.

On 23 April 1770, British explorer James Cook made his first recorded direct observation of indigenous Australians at Brush Island near Bawley Point.

Elections in 1972 resulted in the formation of a ministry headed by Chief Minister Michael Somare, who pledged to lead the country to self-government and then to independence.

A 1958 government leaflet assured readers that unskilled non-British migrants were needed for "labour on rugged projects ...work which is not generally acceptable to Australians or British workers".

When South America eventually separated from Antarctica, the development of the cold Antarctic Circumpolar Current changed weather patterns across the world.

These adaptations are common in species from the large and well-known families Proteaceae (Banksias and Grevilleas), Myrtaceae (Eucalyptus or gum trees, Melaleucas and Callistemons), Fabaceae (Acacias or wattles), and Casuarinaceae (Casuarinas or she-oaks), which are typically found in the Australian mainland.

Even today, pockets of remnant vegetation remain in the cool uplands, some species not much changed from the Gondwanan forms of 60 or 90 million years ago.

The ocean straits between the islands were narrow enough to allow plant dispersal, but served as an effective barrier to exchange of land mammals between Australia–New Guinea and Asia.

[96] This high level of endemism can be attributed to the continent's long geographic isolation, tectonic stability, and the effects of an unusual pattern of climate change on the soil and flora over geological time.

Bird life also flourished—in particular, the songbirds (order Passeriformes, suborder Passeri) are thought to have evolved 50 million years ago in the part of Gondwana that later became Australia, New Zealand, New Guinea, and Antarctica, before radiating into a great number of different forms and then spreading around the globe.

[104] Snow falls frequently on the highlands near the east coast, in the states of Victoria, New South Wales, Tasmania and in the Australian Capital Territory.