Australia: The Land Where Time Began

A biography of the Australian continent 

Palaeozoic Era

At the opening of the Palaeozoic Gondwana was a single landmass, straddling the Equator, on its own continental plate. During the Carboniferous the Tethys Sea opened and Gondwana was swung to the south to become the southern landmass. During this era Asia was in the form a number of separate blocks - China, Siberia and parts of southeast Asia were all separate blocks that converged towards each other and Euramerica, as well as Gondwana, eventually the collision of all these separate blocks merged them into a single giant landmass, Pangaea "one Earth" in the Late Permian. The supercontinent of Pangaea was a stable landmass by the early part of the Mesozoic.

North America collided, and merged with, the western margin of Europe in the late Palaeozoic, at or near the the rift line that formed when the Atlantic Ocean opened. The eastern margin of Europe was at about the region of the present Ural Mountains. When the Asian block collided with the European eastern margin during the Permian, as part of the formation of Pangaea, the sediments that had been accumulating along this margin were raised to form the Ural Mountains.

Considerable differential uplift and subsidence occurred on a large scale in the interior of Gondwana, continuing throughout the Palaeozoic. Deep deposits of sediment were laid down in the major basins that formed at this time, resulting in thick sequences of sedimentary rock.

The Palaeozoic Era has been defined as beginning with the appearance in the fossil record of easily identifiable fossils, in the form of animals with hard parts such as shells and external skeletons that fossilise well. The Cambrian, Ordovician and most of the Silurian, comprise the first 150 million years of the Palaeozoic, covered the time when life was restricted to water. It was during this time that most of the phyla of the Animal Kingdom became established. The Algae represented the Plant Kingdom, being highly evolved and diverse by the Late Silurian, including all classes, ranging from microscopic unicellular plankton to all kinds of seaweeds, that are much more complex - green, brown, red and coralline. Late in the Silurian plants migrated to the land, the first of which are believed to have evolved from and algal ancestor.

When the atmospheric oxygen reached levels that were high enough for ozone to form a layer in the upper atmosphere the land became suitable for land life, as progressively more of the dangerous UV radiation was then filtered out, organisms no longer needing the protection of water. Aquatic photosynthesisers, algae, and before them photosynthetic bacteria and cyanobacteria, had produced the atmospheric oxygen, now the photosynthesising plants could lead the way onto land, modifying the barren environment of the land, producing environments with microclimates suitable for the first transitional animals to survive long enough out of the water to evolve mechanisms to survive away from water. Once the plants had established a beachhead around the water margins the animals could begin to radiate into forms that could move away from the water.

The first animals to leave the water, members of nearly all classes of the arthropod moving to the land, having been partially preadapted to life out of water because of their external skeleton that could also provide a waterproof covering to slow down the loss of water to the atmosphere, as well as protect them from the direct sunlight. It has been suggested that if plants had not succeeded in the transition to terrestrial life the evolution of plants might not have got further than algae, which may have stopped the evolution of vertebrates at the fish stage. By this time algae and fish were highly evolved, having already spread occupied every niche available to then in the water.

 

Sources & Further reading

Mary E. White, 1993, The Nature of Hidden Worlds: Animals and Plants in prehistoric Australia and New Zealand, Reed

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 28/07/2010

 

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading