Just as geologists reconstruct the Earth's past by looking at layers of rock, Antarctic researchers examine layers of ancient ice to discover the secrets of polar history.

Driving hollow tubes as far as 10,000 feet below the surface, scientists retrieve long, layered cylinders of ice, usually about three inches in diameter. These "ice cores" contain compounds that were in the air when the snow that formed them originally fell, as well as everything from dust to radioactive particles.

By analyzing the contents of ice cores, researchers can learn a lot about the environment. Alternating bands of light and dark ice, for instance, correspond to changes in the seasons, and help scientists construct a year-by-year record of changes in local climate, sea level, solar radiation, and chemistry dating back hundreds of thousands of years.

Ice cores from Antarctica have also recorded ecological events that took place thousands of miles away. Some contain evidence of a volcanic eruption that occurred in Indonesia about 73,000 years ago, and samples taken after 1986 showed radioactive traces from the explosion of the Chernobyl nuclear power station in the Ukraine.

To find out more about ice cores
follow these links to activities, information, and timelines:

Stories in the Ice—from a Nova expedition:
http://www.pbs.org/wgbh/nova/warnings/stories/

Secrets of the Ice—Ice cores science performed by the International Trans-Antarctic Scientific Expedition:
http://secretsoftheice.org/icecore/index.html