Australia: Inland Sea and Temperature

What had gone before?

For much of the previous Jurassic period, 208 to 144 million years ago, Australia had been above sea level and was warm and swampy. Australia was still part of Gondwana but during the Jurassic the great continent was beginning to break up and signs of this movement were seen in the outcrops of volcanoes which developed and erupted along Australia’s southern coast – the region where the rift developed. There were large rivers across Australia, with lakes and swamps but Australia was still basically a large landmass.

During the Early Cretaceous, however, a great inland sea swamped the central regions and Australia became a group of large islands. Sea Monsters, plesiosaurs, swam in these inland seas and the whole world became warmer. Australia, now tipped on it’s side lay so that, while the land areas of Queensland lay nearer the equator, the south eastern area was well within the sub-polar region.

Some Jurassic animals and plants survived into the Cretaceous, 144 to 65 million years ago like the Cycads and ginkgos, the labyrinthodont amphibians, some fish and plesiosaurs.

The Cretaceous period

Between the Early and Mid – Cretaceous period the climate, all over the world, became warmer – by perhaps as much as 17° Celsius. The ice caps at the North and South poles melted and became smaller and, of course the water released raised the sea levels all around the globe. Australia had been beginning to break away from Antarctica but, where before it had been more or less one large land-mass, now the water flowed into shallow seas in the centre of the continent. The land that would later become Australia was broken up into a group of islands.

During the Cretaceous period Australia was hot and basically broken up into a number of landmasses separated by great shallow seas. The glaciers had melted and the seas had risen accordingly creating a hot humid existence. That is why many of Australia’s fossil animals were sea-living beasts like Plesiosaurs and Ichthyosaurs..

Were there permanent ice sheets at the South Pole like there are now?

No. Fossils of trees have been found in Antarctica, proving that there couldn’t have been ice there all year round. Trees can’t grow in ice.

Why was Antarctica warmer?

One of the reasons why Antarctica is so cold now is that cold ocean currents flow right around the whole continent. It’s like an enormous fridge. But because South America and Australia were still attached to Antarctica 100 million years ago, strong currents of warm water were probably directed down from the equator, keeping the temperatures up. A climate extreme these days like drought in Australia is caused by the El Nino effect, which is just a slight warming of the surface of the South Pacific. So you can imagine that a really radical change in ocean currents would make an even bigger difference to the weather.

Why was the world so much warmer then?

You’ve probably heard that pollution of the Earth’s atmosphere with too much carbon dioxide causes global warming. Carbon dioxide levels were much higher during the Cretaceous than now. The greenhouse effect has happened before on Earth, only this time it was hotter and caused by volcanoes spewing out tonnes of carbon dioxide and not cars and power plants.

Did the sea level make a difference?

Yes. Warmer temperatures and high sea levels go together. The higher the temperature, the more ice melts and the more water there is. The more water there is, the warmer the planet stays because water changes temperature more slowly than air. It also means that the air is moister and temperatures are more even right around the world

If sea levels were much higher, where is the water now?

100 million years ago sea levels were at their highest for 250 million years. About half of Australia was covered by a shallow inland sea. All of that extra water is now locked away by being frozen solid in the thick polar ice caps.

Was there a big difference in temperature between the tropics and other parts of the world?

There probably wasn’t as big a difference then as there is now. The tropics might have been a bit hotter, but the poles were not as cold as they are now. In other words, the temperature was more even right across the globe.

Mohandas Gandhi

“The weak can never forgive. Forgiveness is the attribute of the strong.”