Greenland was ice-free over a million years ago

Greenland may have been ice-free more than a million years ago, with its bare bedrock exposed for 280,000 years, scientists have found.

During this time, the island's overall ice cover may have dropped by more than 90 per cent.

Previous studies suggested that Greenland's ice shrank in the distant past, but for the first time scientists found how long Greenland endured without its usual frozen cover.

The discovery hints that its surface ice was more variable than once thought - which does not bode well for its future stability in a warming world, researchers said.

Researchers gathered data from isotopes, beryllium 10 and aluminium 26, extracted from bedrock minerals.
 

The isotopes are produced only by cosmic rays, which means that they only occur when the rock that holds them is exposed. These offer clues about when rocks were bare of ice and for how long.

These isotopes originated in the only rocky core ever extracted from land underneath Greenland ice, drilled at the Greenland Ice Sheet (GIS) summit in 1993.

Minerals from this solitary core are second only to moon rocks in their rarity and importance, as they are the only existing evidence of Greenland's extant bedrock, according to Joerg Schaeffer, from the Columbia University's Lamont-Doherty Earth Observatory in the US.

When this core was first examined decades ago, researchers were able to detect isotopes in the sediment produced by cosmic rays, but their equipment was not sensitive enough to gather precise climate data, Schaeffer told 'Live Science'.

In order to get to the isotopes, researchers dissolved minerals with acid so they could observe the atoms.

The research was published in the journal Nature.