Natural history of Australia

The geological history and climatic of the Australia contributed to return its fauna and its single flora.

One still finds in Australia of the areas of very old rocks, called Craton S, going back more than 2.5 billion years, which during the Archéen took part in the constitution of the only continent existing on the surface of the ground at one time when the life started to appear there.

It is:

Craton d' Altjawarra, located about at the center of Australia, at semi distance enters the towns of Alice Springs and Mount Isa. Entirely covered by the sediments with the Cambrien and the Ordovicien with the " Georgina Basin" , it is not apparent any more at present
central Craton
Craton de Curnamona (Australia southernmost)
the Craton de Gawler (center of Australia of the South)
Craton de Pilbara (Australia Western)
Craton d' Yilgarn (Australia Western)
Craton of the Péninsule of Eyre (in the south of southernmost Australia)

Precambrian

Three of these let us cratons play a big role: let us cratons of Yilgarn (in the west), Pilbara (in north) and of Grawler (in the south).

Between 2,500 My and 545 My, during the Protérozoïque, the construction of the Australian continent will continue with the erosion of these cratons and the formation, in periphery, of sedimentary layers which, in consequence of the appearance of oxygen in the air, will contain iron oxide (They are the " Banded Iron beds" , formed sediments of alternate layers of Ore of Iron (ématite) and of Clay, of the Or, the Uranium, the Cuivre, the Plomb, the Zinc which will accumulate by Accrétion. These are the old sediments which explain the presence of many the mines in Australia and the effort of the Australian government for better knowing the nature of its basement.

It seems that these three portions of continent finished, following the tectonic movements, by entering in collision and to take part in the formation of supercontinent Rodinia between 1,3 and 1,1 billion years. Let us cratons northern and western would have initially joined, the southern craton being itself associated only much later (there are there 830 to 750 My whereas the north of supercontinent Rodinia broke. Let us cratons Western initially ran up then those of the south between 830 and 750 My to form a super sedimentary basin, the Centralian Superbasin The archaean rocks of the craton of Pilbara contain the first traces of life. They are Cyanobactérie S primitives known under the name of Stromatolite S. All these plants are watery. The first traces of Arbuste S Lycophytes appear in the Antarctic and Australia.

From 350 My to 140 My

The continents (Gondwana, Euramerica, and Siberia/Angara) which had derived independently end up running up to form the Pangée Dévonien with carboniferous, there are approximately 350 My. This event caused a mixing of flora and fauna. Pangée breaks at the beginning of the Jurassic . The continent is then subjected to one period of glaciation during the Carbonifère, around 330 My, which causes a strong glacial erosion. It is at that time that, in the not very deep basins the layers of coal are formed.

Whereas Lycophytes dominated the flora until the beginning of the carboniferous one, little by little the ferns Pteridospermatophyta or the complexes formed by the Nothorhacopteris - Fedekurtzia - Botrychiopis , replace Lycophytes of the equator to the pole.

During the hotter period of the Mesozoic between 251 to 140 My, the Australian continental masses are covered with river basins. The wet conditions support in particular the appearance of Tourbière S in the east. Many fossils Dinosaur S, Reptile S, Bird X and mammaliens were discovered.

The oldest fossil of known Australian batrachian is species Vieraella herbsti and gone back to 180 My, before the formation of the Gondwana and from Laurasia. Other fossils of this species are gone back to 188 My to 213 My and are found on several current continents, confirming the theory of the continental drift.

Cretaceous

140 million years ago, Gondwana started to break. The Indian family and sychelloise of the Sooglossidae is regarded as close relation of the Australian family of the Myobatrachidae . The Sooglossidae being more narrowly close to the Myobatrachidae than of the African or South American families. What is logical since, the India, Madagascar and the Seychelles separated from Gondwana roughly 130 million years ago. Between 140 and 99 My, the sea recovers most of the grounds and in parallel between 120 and 105 My, of the volcanic phenomena risings in Eastern Australia cause. They create the Mer of Tasmanie in the south east and the Mer of Coral in north. The climate was hot and wet there.

From 65 to 7 My

There are 50 My, Australia separated from the Antarctic and became relatively insulated. The climate changed gradually: a circumpolar Courant the Antarctic about the middle of the era Oligocène (between 30 and 15 My) developed around the Antarctic and in the south of Australia. Precipitations decreased, there was a slow warming of the continent. The Australian climate became more and more arid, giving place to the appearance of various groups organization specialized for this climate, like moisture tropical and seasonal of the coasts birth gave to other specific species. While the climate total cooled and the Antarctic became a frozen ground.

The continental masses Australian is isolated, the migration of the species is then impossible. The establishment and the evolution of the Australian fauna of today was apparently caused by the single climate and the geology of the continent. The single fauna which came from Gondwana, such as the marsupials, survived and is adapted to Australia., pollens discovered shows that the current plants of Australia originate in well the plant of the Austro-Antarctic continent. The Angiosperme S present are the evolutions of the primitive angiospermes southernmost Laurasia and north of Gondwana. Pollens most common being those of the kind Nothofagus . The study of the evolution of pollens between 25 and 10 My makes it possible to imagine the rapid proliferation of species like the Eucalyptus , the Casuarina , the Allocasuarina , the Banksia and the Faboideae , and the replacement of the subtropical forests by sparser forests; the first meadows appeared with the Eocene .

The dryness, the low content of the grounds of nutrients led to the development of a fauna and an original flora. The species of some families adapted well to these conditions, like those of the acacias and of the eucalypti, spread themselves on the continent by giving a great number of species. Thick sheets with a Cuticule, a mechanism of Photosynthesis in C4 for the Dicotylédone S and in CAMWOOD for the Monocotylédone S make it possible the plants to reduce their water losses. The dryness was accompanied by an increase in forest fires and these fires played a part in the appearance, the development and the distribution of species adapted to fires at the end of the Pléistocène.

If the marsupials seem to have emerged during the cretaceous in the northern hemisphere, as leaves it thought the discovery of a fossil of Kokopellia old of 100 My and found in Utah, the first proof of the presence of marsupials on the continent dates from 55 My, i.e. afterwards after the Extinction of the Cretaceous. It was found close to Kingaroy in the Queensland. The marsupials present resembling much those of South America, extremely logically because the two continents were, strong can of front time, in contact. On the same site a Placental mammal about the Condylarthra ( Tingamarra porterorum) . As in America, the marsupials lived with the placental ones and it seems that only the marsupials survived in Australia.

The continental masses of the Australian plate and that of the Eurasia remainder separated by seas except exception to the Miocène there are 5,3 My. This collision allowed the entry of new species like the Lepidium and the Chenopodiaceae . A new fauna of Asian origin also could be established. The Ligne Wallace (hypothetical line separating the zoogeographical écorégions from Asia and Australasia) delimits the border between the Eurasia and the indo-Australian plate. This border continental prevented the formation of a ground connecting Asia and Australia what allowed a distinct distribution zoological, with a limited overlapping, majority of Australian and Asian fauna except for the birds. Interior Australia was covered with river basins and lakes. Fauna were very diverse. Birds, monotrèmes, frogs and snakes are fossil witnesses of this period.

The interior lakes disappeared there are 5 My. Several hot and cold periods during which the sea was discovered between Australia and the New Guinea made it possible the species to migrate of north to the south.

One of the sites of Australian fossils most important for the Miocène and the Oligocène is with Riversleigh in the Queensland.

See also: Deserted Australian, Bush Australian

Holocene Pleistocene and

See also: Mégafaune Australian, Fauna of Australia, Prehistory of Australia, Flora of Australia

The masses of the principal continental masses consisted the Australia island and the New Guinea remained, except exception, separated by seas, making the migration of the species impossible. However, during certain glacial periods, as 10.000 years ago, the circulation of fauna at possible summer between these masses. This was also possible with the Eurasia, for example during the Glaciation of Würm, 50.000 years ago. Thus it is probable that the Litoria caerulea migrated from Australia to New Guinea because of its geographical distribution broad to Australia and very sectorized in New Guinea. Even thing for the species of the kind Nyctimystes . For this same reason, the families of Microhylidae and Ranidae , very present in the northern hemisphere, occupy only extreme Australien north. Two species out of fifty-nine for the Microhylidae , and only one on seven hundred and fifty of Ranidae are considered indigenous in Australia. When they could be established, the majority of the ecological niches were occupied by local batrachians.

The man invaded the continent at the end of pleistocene, there is: 50000 years.

An increase since: 38000 years of wood flarings found in the sediments was correlated with the arrival of the first aboriginals and one thinks that the practice of the densherings played a big role in the development of the sclerophyllous forests especially on the east coast of Australia. The adaptations to fire result in a development of the Lignotuber S and buds epicormic S at the Eucalyptus and the Banksia allow a fast regenation after fire. Some kinds of plants adopted the Sérotinie and release their seeds only with heat and/or smoke. The Xanthorrhoea and some species of orchises flower only after one fire.

See too

Geology of Australia
Geography of Australia

Sources

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