Present-day glacial landscape, Greenland, 1981.

During the Ice Age, complicated interactions between the earth's atmosphere and its oceans caused extensive glaciation during the Pleistocene, or Ice Age. The power, weight, and movement of ice shaped much of the Illinois landscape. During the Ice Age, which lasted from about 1.6 million to 12,000 years ago, mile-thick masses of glacial ice extended into Illinois, moving colossal amounts of rock and earth. When the ice retreated, it left broad, flat, plains, some rolling topography, and gently flowing streams. What was Illinois like when the first Paleoindian people arrived?