Digging a hole on another world may settle a nagging question about Earth's climate. From about 1300 to 1870, much of the Earth is thought to have endured a long cold snap dubbed the Little Ice Age. If such a freeze occurred, it is usually blamed on a dip in solar activity, but there are other suspects such as volcanoes. If the sun was responsible, we should see evidence of it across the solar system, says Ralph Lorenz of the Johns Hopkins University Applied Physics Lab in Laurel, Maryland. To settle the debate, he suggests digging a hole on Mars to see if it, too, had an ice age around that time. Temperature changes spread downward through ice and soil, so a borehole will contain clues about past climate. The ice sheet in Greenland contains evidence of the Little Ice Age at a depth of about 60 metres, for instance. "There is a clear signal of the Little Ice Age there," Lorenz says. "As the surface temperature goes up and down, a thermal wave propagates downward. So the deep interior has a muted memory of it." More via New Scientist.
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