Down but not under

The ocean covered about half the surface area of other continents seventy million years ago. However, Australia managed to stay dry. How did it happen? Geophysicist Michael Gurnis of the California Institute of Technology in Pasadena, USA, may have the answer. During this period, Australia was 250 metres higher than it is today. Gurnis developed a computer model of the movement of tectonic plates and the heat flow in the underlying mantle. He investigated a heavy ocean crust that was dipping beneath eastern Australia about 130 million years ago. His model showed that when this process came to a halt, the country moved over the cold sinking slab that had initially pulled it down. This assumption answers why over half the continent was flooded 120 million years ago. Then Australia bent upwards again, reaching its highest point at a time when global sea levels was at its peak. Since then Australia has moved north and sunk to its present level ( New Scientist , Vol 157, No 2125).

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