DIGGING DOWN AND BACK IN TIME?Each year?s snowfall is stacked up and preserved atop glaciers, forming layers, almost like annual tree rings, as seen here in the receding Quelccaya Ice Cap in the Peruvian Andes Mountains. The ice traps isotopes, gas bubbles, and particles that scientists analyze for evidence of the Earth?s environment long into the past. (Lonnie G. Thompson, The Ohio State University)[back]
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