Geologically, it is the same age as the Americas, Asia,
Africa,
Europe, and Antarctica. Australia's
crust, however, has escaped strong Earth forces in recent geological history, accounting for its relatively uniform appearance. As a result, the continent serves as a window to early geological ages.
About 95 million years ago, tectonic forces (movements and pressures of Earth's crust) split Australia from Antarctica and the southern supercontinent of Gondwanaland. Geologists estimate that the continent is drifting northward at a rate of approximately 18 in (28 cm) per year. They theorize that south Australia was joined to Antarctica at the Antarctic regions of Wilkes Land, including Commonwealth Bay. Over a period of 65 million years, beginning 160 million years ago, Australia's crust was stretched hundreds of miles by tectonics before it finally cleaved from Antarctica.
Testimony to the continental stretching and splitting includes Kangaroo Island off South Australia, made up of volcanic basalts, as well as thick layers of sediment along the coast of Victoria. Other signs are the similar geology of the Antarctic Commonwealth Bay and the Eyre Peninsula of South Australia, especially equivalent rocks, particularly gneisses (metamorphic rocks changed by heat and pressure) of identical age. The thin crust along Australia's southern flank in the Great Australian Bight also points to continental stretch.
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