Abstract
Glaciologists have drilled about a dozen deep ice cores into the Greenland and Antarctic Ice Sheets. The two most important, drilled to about 3000 meters to bedrock from the top of the Greenland Ice Sheet, are the GRIP and GISP2 cores. It is claimed that annual layers of snow and ice, so well marked at the top of the cores, can be counted downward to 2800 meters for a total of 110,000 years in the GISP2 core. The annual layer method is said to be like counting tree rings to determine the age of a tree. (The measurements could not be made below 2800 meters because the annual layer thickness was assumed to be too thin. The 250 meters of ice below this depth is believed to be many hundreds of thousands of years old.)