GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
North American glaciation during the Pleistocene epoch. Throughout Earth's history, there have been repeated episodes of cooling of the climate (ice ages), accompanied by periods of advancing ice sheets or glaciation. The last major glaciations took place during the Pleistocene, from 1.8 million to 11,000 years ago. This image shows the ice at its maximum extent, when it reached a latitude of 40 degrees North, about a million years ago. The depth of the ice was over 1.5 kilometres. To the South, the cooling produced mountain glaciers, enormous lakes and a lowered sea level.
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