Australia: The Land Where Time Began

A biography of the Australian continent 

Australia - Physique

Australia is an extensive though low continent, about 7.66 millionn km2 in area, with a mean altitude of only 330 m above sea level of the present, and 40 % of the surface area is less than 200 m above sea level, and Mt Kosciuszko, its highest point, has an altitude of only 2227 m. Even the much smaller landmass of New Zealand has Mt Cook (Aoraki) with an altitude of 3374 m. Mt McKinley in the North America is 6194 m above sea level, and at least 50 of the highest mountains in the world have altitudes of more than 7,000 m. So compared with these other continents Australia is remarkably flat.

As Australia has few major islands, inlets or embayments it is regarded as a compact continent. Its coastline is just less than 20,000 km, the ratio of shore length to land area is 1:390, compared to the ratio of peninsula and insula Europe of 1:75. The Gulf of Carpentaria, Bonaparte Gulf  and King Sound along the north coast, on the west coast Shark Bay and Exmouth Gulf, and on the south coast Port Phillip Bay, the Gulf of St Vincent and Spencer Gulf. The only major islands are Tasmania and Kangaroo Island to the south, Fraser Island to the east, and Groote Eylandt, Melville Island and Bathurst Island to the north. Endorheic streams (flowing inland and not to the seas) serve more than half of the continent, flowing to internal drainage basins. The Lake Eyre catchment covers 1.3 million km2 in central and northeastern Australia. Exhoreic streams (rivers that flow to the sea) service less than half of the continent, and of these only the River Murray is notably long, though it has a low discharge for the size of its catchment.

Geological Framework

Australia has ancient massifs or shields composed of crystalline rocks that are billions of years old, as do all other continents. Included in many of these are zones of sedimentary rocks, some of which are unexpectedly undisturbed, though most of the them have been contorted in ancient fold belts or orogens. There are several sedimentary basins of various ages, some of which are seriously deformed at depth, that underlie the Great Artesian Basin, a feature from the Mesozoic, comprised of the Eromanga Basin, Surat Basin and the Carpentaria Basin. They form a series of structural platforms, or regions of relatively undisturbed strata, together with the Murray Basin, extending from the northern coast to the southern coast.

Within the shield areas remnants of old orogens and platforms occur as outliers. They constitute the various cratons when taken together. The terms 'craton' and 'block' are virtually synonymous, but following Trendall (1990, pp. 3.7), 'block', used in this context, denotes a relatively stable crustal unit that has evidently been a tectonic high at all times, in contrast to adjacent basins that are consistently depressed.

Australia is an ancient continent, geologically. The Earth has been shown by physical dating to have formed 4.5-4.6 Ga (e.g. Dalrymple, 1991). Many meteorites are of that order of age, though Moon rocks have been found to have formed about 3.5 Ga. Many of the rocks that have been exposed in the western shield lands of Australia have been dated to more than 4 Ga (Wilde et al., 2001; Laeter & Trendall, 2002), making them among the oldest analysed from anywhere in the world. See Jack Hills. The dates have been obtained from zircon grains in exposed quartzites near Mt Narryer, in the catchment of the Murchison River of the northern Yilgarn Craton. The quartzite crystals were produced by the weathering and erosion of older rock, which has not been located. There is the possibility here of finding rocks older than the oldest dated so far, though it may have been completely destroyed by natural forces.

There are also alleged signs of former life, fossilised bacteria or bacteria-like organisms (prokaryotes that are from about 3.4 Ga) that have been discovered in the Mt Narryer area (Schopf & Packer, 1987; Rasmussen, 2000) but see also (Brazier et al., 2002). Eukaryotes, complex single-celled organisms have been found in the same area dating from about 3.1 Ga. Australia therefore has rocks and organisms that are as old or older than any found to date.

Sources & Further reading

  1. Twidale, C.R., 2007, Ancient Australian Landscapes, Rosenberg Publishing Pty. Ltd. , NSW
Author: M. H. Monroe
Last updated  30/10/2013
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