In terms of geology, 10,000 years is the same as a blink of an eye in a lifetime. However, there have been many changes in what is now Illinois, compared to what it was that long ago.
Imagine going back to that time. The climate has just begun to warm up, after experiencing a period when glaciers entered the state. Ice sheets are still as close as southern Canada. The Great Lakes are beginning to form as the ice continues to melt. The Illinois River is a relatively new river, especially in the northern part of the state. The lower part of the Illinois River has taken the place of the ancient Mississippi River, which moved farther west during the glacial advance.
The type of plants in Illinois is changing from sparse tundra (a cold semi desert) to grasslands in the northern part of the state, and from spruce to oak-hickory forests in the southern part of the state. Because these changes were occurring so quickly, some scientists believe many living things could not adapt. They had to move to other areas, or cease to exist around this time.
There were several types of animals present then that can no longer be found in this area. Some have become completely extinct.
Two large animals that inhabited the Midwest, Mammoths and Mastodons, are examples of two creatures that could not survive the changes that were taking place.
Mammoths were much like today's elephants that are found in Africa and India.
Mastodons, while looking much like an elephant, were different in several respects (see Mammoths and Mastodons).
Other large animals that were present included ground sloths, giant beavers, and bison.
As the climate continued to warm, ecosystems changed. An Ecosystem is an interacting community of organisms and their environment.
New plants took over areas previously dominated by cold weather plants. Animals that had previously relied on these plants for food had to move to other locations, which meant that predators that relied on these animals for food had to move as well. Sometimes there was no place that provided satisfactory food and shelter. Eventually, many of the Ice Age animals became extinct.