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The Ice Age
The Pleistocene, or Ice Age, began over 2.5 million years ago and ended a short 10,000 years ago. During this time, numerous ice sheets formed and moved south from Canada into the United States. Periodically the climate warmed and the glaciers receded, only to form and surge south again.
Why was there an Ice Age?
Large land masses near the poles created a surface upon which thick ice could form.
The formation of mountain ranges caused major climatic change by shifting global circulation patterns.
Decrease in atmospheric carbon dioxide reduces the insulating effect of the Earth's atmosphere, resulting in heat loss.
Changes in the position of the North Pole and the Earth's tilt and orbit around the sun affect how much solar radiation it received.
The Last Ice Age
Links to the Iowa Department of Natural Resources' Geological Survey:
They Came to North America
There was no single event or condition that allowed for human arrival and settlement in North America. Humans probably arrived here in small groups, and families soon spread across all of North America.
How Did They Get Here?
The Ice-Free Corridor:
Sea Coast Migration:
The Atlantic Route:
Des Moines 16,000 Years Ago
Des Moines 16,000 years ago was a place of contrasts. At times, the ice front of the Des Moines Lobe surged to the north edge of the Raccoon River Valley and then retreated. The ice stood hundreds of feet high. Sediment choked the Raccoon River, backing up the water and splitting the channel into interlacing braids. At other times the volume of melt waters increased and the current was deep, fast, and abrasive.
This area was a mix of grasslands and forests of spruce, aspen, and oak. Stretching north of Des Moines, in areas where the ice had melted, marshes and muskeg (or bogs) were common. This environment supported a variety of herbivores.
Fossils from the time reveal that the Des Moines region was home to mammoth, mastodon, giant ground sloth, musk ox, a variety of bison, and elk. We do not know for certain if humans walked the Raccoon River Valley at this time, but they may have. We do know that soon they would be in Iowa and surrounding states, hunting the mammoth, mastodon, and other game.
Within a few centuries, the temperatures warmed and the ice melted for the last time. New forests filled the river valleys, prairies stretched out to the west and south, and marshlands continued to the north. The subtle changes brought great change to the inhabitants—extinction for some, and opportunity for others.
How Do You Make a Mammoth?
The life-size cast of the Hebior mammoth was produced by PAST: Prehistoric Animal Structures, Inc., of East Coulee, Alberta, Canada. The molds for the cast were made from the original fossilized skeleton discovered in 1994 on the Hebior farm near Lake Michigan. Because the Hebior mammoth was 90 percent complete, some missing or damaged bones had to be created.
Candid shots show step by step how the skeleton was made and moved, from Canada to our museum.