A record of ice sheet demise

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Science  10 Nov 2017:
Vol. 358, Issue 6364, pp. 721-722
DOI: 10.1126/science.aaq1179

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The Cordilleran ice sheet once covered nearly all of western Canada, from the Puget Lowland of Washington to the southern reaches of Alaska (1). Unlike the Laurentide ice sheet, which covered the relatively flat Canadian shield of eastern Canada, the Cordilleran ice sheet blanketed the high alpine peaks of the Canadian Rockies and Coast Ranges. Although relatively small (2), it was nonetheless important for shaping the landscape. It also played a critical role in paleohuman migration from Asia to North America (3) and potentially in past rapid climate events (4). However, the timing and style of the ice sheet's final demise after the last ice age have been unclear. On page 781 of this issue, Menounos et al. (5) provide an extensive chronology of Cordilleran ice sheet deglaciation.