Scientists believe they have found the world's oldest ice sheet, which will provide information on future climate change.

The discovery, made in eastern Antarctica, is 1.5 million years old, almost twice the age of the previous oldest sample.

It follows five years of research and field work, involving scientists from 22 countries.

Dr Tas van Ommen, from the Australian Antarctic Division, says airborne radars were used to shine light through the ice and reveal its thickness.

"There are large areas of east Antarctica where we really didn't know anything about the ice thickness or at least very little. There were big voids in the coverage," he said.

"We've had a cooperative project between the US and the UK using old DC-3 aircraft flying out of Casey station and mapping bedrock underneath ice over a very large area called Aurora Basin.

"We used information we had from existing ice cores, estimates of the heat coming up from the earth, the geothermal heat, then some of the team ran very detailed models of how the ice flows to look at how old the ice would be."

The ice sheet is about three kilometres thick.

Dr van Ommen says an ice core taken from the sheet could hold valuable information about the earth's climate and greenhouse gases.

"An old ice core, over a million years old, would tell us more about how the climate responds to CO2 levels, and we can then use that information to understand how it is going to change in the future," he said.

Scientists say the discovery is also significant for future ice-core exploration.

The study's lead author is Hubertus Fischer, a climate physics professor from the University of Bern in Switzerland.

He says a deep drilling project in Antarctica could commence within three to five years.

"This time would also be needed to plan the drilling logistically and create the funding for such an exciting large-scale international project," he said.

The research findings have been published in the journal Climate of the Past.