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Ice cores provide excellent seasonal markers allowing very accurate dating.

Seasonal markers such as stable isotope ratios of water vary depending on temperature and can reveal warmer and colder periods of the year.

For six weeks every summer between 19, Alley and other scientists pushed columns of ice along the science assembly line, labeling and analyzing the snow for information about past climate, then packaging it to be sent for further analysis and cold storage at the National Ice Core Laboratory in Denver, Colorado.

Nearby, a specially built drill bored into the thick ice sheet twenty-four hours a day under the perpetual Arctic sun.

Analysis of the physical and chemical properties of an ice core can reveal past variations in climate ranging from seasons to hundreds of thousands of years.

Ice core records can be used to reconstruct temperature, atmospheric circulation strength, precipitation, ocean volume, atmospheric dust, volcanic eruptions, solar variability, marine biological productivity, sea ice and desert extent, and forest fires.

Based on flow models, the variation of oxygen isotopes, the concentration of carbon dioxide in trapped air bubbles, the presence of oxygen isotopes, acid concentrations, and particulates, they believe the lowest layers of the ice sheets were laid down over 160,000 years ago.

Annual oscillations of such quantities are often evident in the record. Do they cause a problem for the recent-creation model of earth history? This article will show that the great ages reported for the bottom layers of ice sheets depend on assumed models of past climate and are not the result of direct counting of layers.

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Summer brings 24 hours of sunlight to the polar regions, and the top layer of the snow changes in texture—not melting exactly, but changing enough to be different from the snow it covers.

by Holli Riebeek· design by Robert Simmon· December 19, 2005 Richard Alley might have envied paleoceanographer Jerry Mc Manus’ warm, ship-board lab.

(See previous installment: “A Record from the Deep.”) One of the researchers in the Greenland Ice Sheet Project 2 (GISP2), Alley huddled in a narrow lab cut into the Greenland Ice Sheet, where “the temperature stayed at a ‘comfortable’ twenty below [Fahrenheit],” he wrote in his book about his research, An assembly line of science equipment lined the twenty-foot-deep trench that served as a makeshift lab.

) can be used to identify input from volcanic sources.

The 1815 Tambora Eruption, responsible for the “year without a summer”, is a commonly used “dating horizon” that has been found in ice cores around the Earth.