Australia: The Land Where Time Began
The Great Journey North
- Stages Along the Way
Some of the stages along the way from Antarctica to the present position near Asia
44 Million years ago
At this time Alice Springs was at latitude 45o South. A cold ocean current moved north along the West Australian coast and a warm ocean current moved south along the east coast. Northern Australia had reached the desert latitudes, but the rainfall was maintained at adequate levels by warm ocean currents. The continent was still dominated by Nothofagus forests as it had been when part of Gondwana, but Banksia and Casuarina were becoming more common. At this time the first eucalypts and grasses appeared.
21 million years ago
Alice Springs was now at latitude 32o south. The circum-polar ocean currents were firmly established and Antarctica had began to become glaciated. In central Australia there was enough rain to support woodlands and permanent lakes. Nothofagus and rainforests are now confined to the coasts and other favourable habitats. The first chenopods and Acacia have appeared in the fossil record. Cold ocean currents now passed north along the West Australian coast and east along the southern margin of the continent, while warm currents still pass south along the east coast.
10 million years ago
Antarctica was now covered by a single sheet of ice. The direction of the cold and warm ocean currents are unchanged, but now the warm eastern current is being deflected north past New Zealand. Circulation patterns in oceans and atmosphere are now similar to the present patterns. Central Australia was drying out and was now semi-arid. The inland was dominated by woodlands, shrublands and grasses.
18,000 years ago
This was the height of the most recent of a series of glacial periods characteristic of the present ice age. It was a time of extreme aridity in central Australia. Dust plumes from central Australian deserts were blowing north-west from the Australian west coast into the Indian Ocean, and east across the east coast as far south as Tasmania into the Tasman Sea, and sand dunes were active in central Australia. This was a time of extinction. After the peak of the glacial period the climate improved for the last 200 years. Since white settlement the extinction rate has again increased.
The present time is an interglacial period, and southern Australia has predominantly winter rainfall, while northern Australia has a mostly summer rainfall. In central Australia the climate has ameliorated since the peak of the latest glacial period, but the average rainfall of 250 mm/year is unpredictable and erratic. At the present the sand dunes of the central deserts are stable and the arid areas support woodland, shrubland and grassland.
After the Greening, The Browning of Australia, Mary E. White, Kangaroo Press, 1994
|Author: M.H.Monroe Email: email@example.com Sources & Further reading|