Since 1974 scientists at Russia's Vostok ice station situated at the very center of Antarctica have been extracting ice cores from the polar ice cap. Drilling down 12,000 ft (3600 metres) they have brought to the surface ice that was formed 400,000 years ago.

American and Russian scientists examine microbe

When the ancient ice is melted and passed through fine-mesh filters microbes are extracted. Studying such microbes may help scientists understand the evolution of life on Earth and how to search other worlds for signs of life.

Antarctic microbe

"We're exploring a new world," says Richard Hoover of NASA who is assisting the Russians. Over 400,000 years bacteria could have undergone significant evolutionary changes. Comparing modern and ancient bacteria could throw new light on how they have evolved.

It is well known that bacteria can survive for hundreds of thousands of years in the permafrost of Siberia so there is a chance that scientists could coax the ancient bacteria back to life.

Europa, an ice-moon of Jupiter

Beneath the ice under Vostok station lies an underground lake. Cut off for possibly millions of years it may contain forms of life that have been isolated from outside influence. So far scientists have stopped drilling 300 ft (90 metres) above the lake to avoid contaminating it.