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Several sites in and around Illinois provide continuous records of changing plant communities from the end of the last Ice Age to today. Ice reached its maximum extent about 24,000 years ago, and retreated from the state by about 17,000 years ago. Since then pollen has been collecting in annual layers as it has fallen into bogs and lakes.
Learn about how scientists who study pollen (palynologists) take sediment cores and analyze them. (use the back button to return here) After counting the fossil pollen species at different levels in one site, scientists can make a chart that gives a picture of the changes in the forest over a long period of time. The next section shows a pollen diagram for Nelson Lake. Pollen has been preserved there continuously since 18,000 years ago.
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