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Living remnants of early life in Australia

23 May 2013

We have learned much about the early history of the Earth from fossil and living remnants of life. The crust of the Earth supports ever-moving tectonic plates that join, separate and move about. In this way various Supercontinents have formed since Ur first formed 3600 million years ago only to rift apart again. Ur contained portions of what is now Canada; northern Siberia and Greenland; north-eastern Antarctica; India and Atlantica. The latter contained parts of Africa, Australia and Madagascar. The Supercontinent Gondwana formed 600 million years ago and Australia was initially part of its eastern edge with what is now eastern Australia near the equator and western Australia closest to the South Pole.

www.leopard.tvBecause the southern polar ice only started to form some 45 million years ago when Australia was the last tectonic plate to break away from Antarctica, Australia still contains remnants of the rainforests which once covered Gondwana. These remnant Australian rainforests are now World Heritage Sites because they are a living record of early forms of life, a window to the future and biodiversity hotspots with many rare forms of life. They survived because Australia has been isolated for 45 million years as an island continent

The huge Tweed volcano which erupted from 23 to 20 million years ago on the Gold Coast of Australia created a mountain that was 2 km high and a caldera some 1 km deep and 40 km in diameter, the largest in die southern hemisphere. This region receives some 3000 mm of rain per year and contains remnants of the Godwana rainforests with trees such as the Arctic beech Nothofagus moorei that also once grew on Antarctica. The Natural Bridge Cave in The Springbrook National Park in this old caldera contains one of the scattered and isolated glow worm colonies that migrated with Australia when it broke away from the Antarctica. These are the larvae of the insect Arachnocampa flora and only the female glows to attract a mate for reproduction.

Australia contains other remarkable living forms of early life, including some of the few living colonies of stromatolites which are the earliest known forms of life on Earth which is currently estimated to be 4.6 billion years old. Initially the Earth was covered in molten lava which gradually cooled, while the atmosphere contained hydrogen that came from solar nebulae. Carbon dioxide, nitrogen and water then degassed from the Earth’s interior to cover the Earth’s surface with shallow oceans and to form an atmosphere that contained mainly nitrogen and carbon dioxide. Blue-green algae first developed some 3.5 billion years ago in the shallow oceans while the first land mass only formed 1.5 billion years ago and was  only some 100 m above the ocean surface in most places. These algae have the ability to extract carbon dioxide from, and through photosynthesis to release oxygen into the water. Over time this led to the development of many forms of life in the primordial oceans. This process also caused the precipitation of calcium carbonate which adhered to the slimy bacterial layer to form a base upon which new colonies of bacteria grew. This gradually built up successive layers of rock-like calcium carbonate that were continually topped with a living colony of algae and are known as stromatolites. The stromatolites increased in the initially shallow oceans and eventually released enough oxygen into the atmosphere to support terrestrial life.

The oldest evidence of such blue-green algae is found in the rocks of the Black Reef Formation of the Barberton Mountains of South Africa that are some 3.5 billion years old. These rocks formed in the shallow former Transvaal Sea in a geological formation that is similar to the Great Barrier Reef of Australia. When the oceans became deeper as the land masses developed through volcanic action and rifting while grazing marine life proliferated, many colonies of blue-green algae died off. However, a few colonies survived in isolated, shallow estuaries with a high salinity. A thriving colony... (To read and see more become a Green subscriber)

 

References:

2012. Shark Bay. http://en.wikipedia.org/wiki/Shark_Bay

McCarthy T and B Rubidge 2005. The Story of Life & Earth. Cape Town: Struik Nature.

Unesco 2010. The Gondwana rainforests of Australia World Heritage Area (extension to existing property). http://whc.unesco.org/en/tentativelists/5541/

By: Prof J du P Bothma

 

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