From the outside, the storage shed on the University of New Hampshire (UNH) campus in Durham looks inconspicuous enough-a standard white 48-by-12-foot box. It doesn't look too remarkable from the inside, either, housing a few electric jigsaws and racks holding thousands of cylindrical canisters filled with ice. This is not your average ice locker, however. It contains all the pieces of a two-mile strip of ice drilled from a massive ice sheet in Greenland. Moreover, this ice holds vital data about the earth's climate over the past 250,000 years and offers the most detailed record yet of the last 110,000 years of our planet's history.

"In some ways, the ice sheets tell us more about what the environment was like in northern latitudes 100,000 years ago than we can learn about the 1700s and 1800s from human records," says Paul Mayewski, director of glacial research at UNH and chief scientist for the Greenland Ice Sheet Project Two (GISP2). "Those written records consist mainly of temperature readings, but we can use the ice to analyze 45 different variables."

Mayewski views the ice sheets as a "time machine" that not only tells us about the earth's history, including the effects of hundreds of volcanic eruptions, but also about human history. This frozen repository is providing a bounty of information to both earth scientists and archaeologists.

How can they extract so much information from ordinary chunks of ice? The Greenland ice sheets are composed of snow that falls to earth carrying compounds from the air, including chemicals, metals, dust, even radioactive fallout. The snow piles up layer by layer, year after year, trapping these substances. Pressure from the accumulating snow eventually creates ice, and bubbles that form in the ice seal off small samples of the atmosphere. In laboratories at UNH and elsewhere, scientists can precisely identify the yearly layers in the ice-like the rings in a tree trunk-to determine the composition of the atmosphere at that time.