A sample from an ice core drilled in 1993 from the Greenland Ice Sheet has finally been examined, and it was found that the silt and sand at the bottom of the core were deposited 2.7 million years ago. This is interesting because it means the Greenland Ice Sheet never fully melted during the warm periods between Earth's ice ages. Before the ice sheet formed, the soils were covered in tundra for 200,000 years to 1 million years. This landscape was very stable, since it lasted for so long before being covered in ice.
http://www.nbcnews.com/science/science-news/2-7-million-year-old-soil-found-deep-beneath-greenlands-n83596
http://www.nbcnews.com/science/science-news/2-7-million-year-old-soil-found-deep-beneath-greenlands-n83596