Scientists have drilled through the central Greenland ice cap, obtaining an ice core that records climate data for the past 120,000 years.
By Dr David Whitehouse
BBC News Online science editor
They reached bedrock at 0815 GMT on 17 July after seven years, and 3,000 metres, of drilling in one of the remotest spots on Earth.
Champagne on ice
Air bubbles in the core will tell them how the climate has changed over the entire period - right through the last major ice age.
And meltwater obtained from beneath the ice cap may contain microbes that have been isolated from the outside world for hundreds of thousands of years.
The North Greenland Ice-Core Project (NGrip) is situated in the middle of the Greenland ice sheet, on a high plateau of stable ice.
Sub-surface radar observations of the region made from aircraft indicated that it would be an ideal place to drill a hole through the sheet.
The goal was to recover ice frozen 120,000 years ago, from before the last major ice age, when the world was warmer than it is today.
There are important questions to be answered about the global climate over the intervening period. What happened before the onset of the last ice age? Was the start of the cold spell sudden or gradual?
The two ice cores drilled elsewhere in Greenland have been equivocal. One said the transition was smooth, the other suggested it was sudden, presaged by large, rapid swings in climate.
Warm periods between ice ages typically last about 10,000 years. As it has been about 12,000 years since the end of the last glacial period, identifying the signs of a forthcoming ice age is important.
Hence the need for NGrip and a third ice core.
'Wonderful to reach the bottom'
For three months each summer, a team of European scientists, led by Danes, flew into the small base on a Hercules transport aircraft and endured the harsh conditions so that they could delve a little deeper into the ice.
Now, they have achieved their goal. Bedrock was reached at a depth of precisely 3,084.99 metres.
"It was wonderful to reach the bottom and see the frozen mud come rising up to the surface," Dorthe Dahl-Jensen, one of the scientists who supervised the drilling, told Greenland's radio.
"We wept with emotion. It was quite incredible to reach the end, and I will never forget it," said the professor from Copenhagen's Niels Bohr Institute.
The sub-glacial meltwater froze into brownish ice as it was brought up the borehole.
It might contain microbes that have been isolated beneath the ice cap for hundreds of thousands, if not millions, of years.
The core itself contains a wealth of information about climate conditions in Greenland before the last ice age thanks to air bubbles trapped inside.
Catalogued and awaiting analysis
These will yield data about the changes over time in temperature, precipitation and the levels of the different gases in the atmosphere.
But it will be a while before scientists can get to work on the ice samples.
The core has to be stored for a year before it can be sliced into sections. This is to allow the ice to reach equilibrium with the surface conditions after spending tens of thousand of years under intense pressure.