Greenland's ice may hold the key to the puzzle over the climate on the island. To unravel its mysteries, a three-km-deep hole has been drilled in the middle of Greenland. The goal of the project conducted by Danish researchers is to extract an ice core that will reveal how the climate on the world's largest island has varied over the last 1,60,000 years. The Greenland ice sheet is made from layers of snow that over the millennia have been compacted into ice. Researchers are determining the temperature of the ice at the time it hardened, by analysing the ratio of radio isotopes in the ice.