Australia

Of the seven continents, Australia is the flattest, smallest, and except for Antarctica, the most arid. Including the southeastern island of Tasmania, the island continent is roughly equal in area to the United States, excluding Alaska and Hawaii. Millions of years of geographic isolation from other landmasses accounts for Australia's unique animal species, notably marsupial mammals like the kangaroo, egg laying mammals like the platypus, and the flightless emu bird. Excluding folded structures (areas warped by geologic forces) along Australia's east coast, patches of the northern coastline and the relatively lush island of Tasmania, the continent is mostly dry, bleak, and inhospitable.

Other major mountain ranges rise in the eastern section of South Australia near Adelaide: the Flinders and Mount Lofty Ranges. These mountains arose from the Adelaidian Geosyncline (another large trough upon which sediments have been deposited) and were first uplifted over 500 million years ago during the Cambrian and Ordovician eras. Further thrusting occurred more recently, about 200 million years ago during the Mesozoic era.

In parts of Western Australia, particularly the Carnarvon Basin at the mouth of the Gascoyne River, glacial sediments are as thick as three miles. Western Australia, particularly along the coast, has been inundated repeatedly by the sea and has been described by geologists as a mobile shelf area. This is reflected in the alternating strata of deposited marine and non-marine layers.

During the early to mid-Jurassic period, there was an intrusion of 2,000 cubic miles of dark, layered volcanic rocks in Tasmania, similar to the magmatic formations Ayers Rock, central Australia, 1,143 ft (349 m) high. JLM Visuals. Reproduced by permission. of the Karroo region in South Africa and the Palisades in New York. Tasmania separated from mainland Australia only 10,000 years ago, when sea levels rose after the thawing of the last ice age.

The climatological record of Australia shows a pronounced temperature drop on the continent in the late Miocene and early Pliocene epochs between 26 and five million years ago when monkeys and early apes first evolved and saber toothed cats prowled the earth. On the Eyre Peninsula in South Australia and in Gippsland in Victoria, eucalyptus and acacia trees supplanted the previously dominant beech trees that had thrived in the warmer climate of the Miocene era.