46. Ice Sheets (1890s)
Over the past 2.6 million years, most of Canada has been periodically covered by ice during what is called the Ice Age. This was a period of extreme climatic fluctuations that caused the ice to advance and retreat cyclically, and the ice thickness to vary considerably. At times, ice sheets several kilometres thick covering areas the size of Greenland spawned glaciers that extended out like tentacles, molding and radically changing the landscape. The idea that glaciers and ice sheets once covered huge areas of North America was contentious until the mid-19th century.
Fieldwork by pioneering Geological Survey of Canada geologists such as William Logan, Joseph Tyrrell, and George Dawson provided compelling evidence for the presence of ice over much of Canada. Indeed, it was Dawson who recognized and named the Cordilleran and Laurentide ice sheets – terms still in use today.
Between 20,000 and 18,000 years ago, the Cordilleran ice sheet covered most of Canada west of the Prairies. It attained a thickness of about two kilometres, and it briefly fused with the Laurentide ice sheet in the east. The retreat of the ice sheets was rapid, geologically speaking, taking only about 4,000 years.
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