The small window of opportunity comes in spring when temperatures are warm enough to melt the diesel to power the drilling-rig but not warm enough to break up the ice on which the rig is mounted at McMurdo Sound in Antarctica.

For three years, School of Physical Sciences Professor Chris Fielding was part of a seven-nation team that drilled through the sea-ice cap, passed through a 200-metre water column before hitting the sea-floor and penetrating nearly one kilometre into the Earth's crust.

This huge multi-national scientific drilling program, estimated to have cost $US6 million, has yielded columns of data recorded in the rocks beneath the sea.

Dr Fielding says the core samples, collected during the spring of 1997­-1999, contain firm evidence that climate changes have occurred naturally for millions of years.

Recognition of the importance of this project to the current global warming debate has come in the publication of results in a recent issue of the prestigious Nature magazine.

Dr Fielding was one of 33 authors of the paper documenting several cycles of climate change over tens of thousands of years in the Antarctic region, dating back 24 million years.

The drill core contains a chronological record of the sediments shed from the Transantarctic Mountains and deposited in the floor of the Ross Sea.

"The layering we see in the rocks records advances and retreats of glaciers that were driven by temperature changes," Dr Fielding said.

"People equate warming of the Earth now with melting of ice-caps but our data is showing that this need not be the case. We have already found, for example, that the temperatures in Antarctica were once warm and moist enough to support the growth of trees such as pines."

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