Gondwana
Following the breakup of Rodinia; Australia, India and Antarctica made up a large landmass. During plate movements from 750 to 500 Ma South America and Africa moved toward India and Australia and by 500 Ma South America and Africa had joined with them to form Gondwana.
During the Palaeozoic, 545 to 251 Ma, the present landmass of Australia saw two stages of geological development. From 545 to 390 Ma shallow warm seas covered parts of central Australia, with a series of volcanic arcs and deep water sedimentation in the east. During this period between 480 to 460 Ma the Larapinta Seaway extended across the centre of Australia. Cycles of sedimentation and volcanism formed new continental crust, forming eastern Australia. There was a major orogeny in eastern Australia from 387 to 360 Ma. The continent was affected by glaciation around 330 Ma.
The continents that had drifted apart from Rodinia drifted together again during the Paleozoic: Gondwana, Euramerica, and Siberia/Angara collided to form the supercontinent of Pangea during the Devonian and Carboniferous periods, some 350 million years ago. Pangea was a short-lived supercontinent; it began to break apart again in the early Jurassic. While Pangea existed it created opportunities for intermixing of the flora and fauna.
During the Carboniferous glaciation, erosion by ice extended into the Early Permian. Crustal extension and subsidence around 295 Ma formed shallow basins in which thick coal deposits were formed.
During the Mesozoic, when the Earth became much warmer, 251 to 140 Ma, the Australian landmass was covered with riverine plains. Humid conditions allowed the formation of peatlands, particularly in the east. Dinosaurs, reptiles and primitive mammals were present in Australia. Between 140 and 99 Ma sea levels rose and much of the continent was covered. In the same period (between 120 - 105 Ma) there was more volcanism in eastern Australia, leading to uplift creating the Tasman Sea to the southeast and the Coral Sea to the north.
The earliest land plants preserved in Australia occur in desposits from the Upper Silurian and the Lower Devonian in marine sediments in Victoria, named the Baragwanathia Assemblage for its most prominent element, the simple vascular plant the lycopod Baragwanathia. The assemblage also included Rhyniophyta, Zosterophyllophyta, Trimerophyta in addition to other lycopods. All these plants were herbaceous, coastal and required an aqueous environment for reproduction. During the Devonian the first shrub-sized to tree-sized lycopods appeared in Australia and Antarctica; they dominated the flora until the Early Carboniferous. In the mid- to Late Carboniferous, as Australia drifted from equatorial latitudes to polar latitudes, the lycopods waned and were replaced by seed-ferns, and the Nothorhacopteris-Fedekurtzia-Botrychiopis complex.
Most of the modern Australian fauna had its origin in the Cretaceous. From pollen records from the Late Cretaceous it is proposed that the flora of the Cretaceous either evolved within the Austro-Antarctic region or entered Australia from Antarctica. Angiosperms evolved in the northern Gondwana/southern Laurasia during the Early Creteaceous and radiated worldwide, prominent members of this early angiosperm flora were the Nothofagus.
Fossils found at Lightning Ridge, New South Wales suggest that 110 million years ago Australia supported a number of different monotremes, but did not support any marsupials. Marsupials appear to have evolved during the Cretaceous in the contemporary northern hemisphere, to judge from a 100 million-year-old marsupial fossil, Kokopellia, found in the badlands of Utah. Marsupials would have then have spread to South America and Gondwana. The first evidence of marsupials in Australia comes from the Tertiary, and was found at a 55 million-year-old fossil site at Murgon, near Kingaroy in southern Queensland. The Murgon fossil site has yielded a range of marsupial fossils, many with strong South American connections — unsurprising since the two continents were both a part of Gondwana. At Murgon evidence of a placental mammal, a Condylarth (Tingamarra porterorum), was discovered. Placental mammals were also found in North America and South America at this time. This find suggests that placental mammals did coexist with marsupials lived in Australia in the early Tertiary, although only marsupials persisted.
Read more about this topic: Natural History Of Australia