"Schaefer’s team analyzed bedrock collected near Summit from the very bottom of an ice core hole. By measuring radioactive isotopes, Shaefer could estimate how long the bedrock was exposed at or near the surface and then buried by the ice sheet. When cosmic rays pummel Earth’s surface, they interact with the nucleus of surrounding atoms, expelling protons and neutrons from that atom and creating new particles. These so-called nuclides do not naturally occur in Greenland’s bedrock. And being radioactive, they act as nature’s clock, letting scientists infer how long the surface was ice free.
The results show that the Greenland Ice Sheet was ice free for at least 280,000 years, over the last 1.4 million years. Bierman and Schaefer’s studies do not necessarily contradict each other. The sediment below Summit was not fully eroded either during the ice sheet’s retreat or its return. "
This is consistent with other work on cosmigenic isotopes that support the solar activity influences weather here on Earth to the amazement of those who never leave the ivory tower.
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