Any boring taken from the Arctic and Antarctic polar ice caps, containing layers of compacted ice, useful for the reconstruction of paleoenvironments and paleoclimatology and as a method of absolute dating. Continuous cores, sometimes taken to the bedrock below, allow the sampling of an ice sheet through its entire history of accumulation. Because there is no melting, the layered structure of the ice preserves a continuous record of snow accumulation and chemistry, air temperature and chemistry, and fallout from volcanic, terrestrial, marine, cosmic, and man-made sources. Actual samples of ancient atmospheres are trapped in air bubbles within the ice. This record extends back more than 300,000 years.