Forces of Change in Underwater Illinois
The Earth's continents lie on different plates or sections of the Earth's surface. The plates float on the molten layers beneath them. Five hundred million years ago, the plate containing Illinois was located south of the equator.
Sediments build up in marine environments. Over time, they form layers of sedimentary bedrock. In Illinois, these layers are hundreds of meters thick.
Extinction and Evolution
Extinction is the rule rather than the exception. 500 million years ago a large number of species died out in a major extinction event at the end of the Cambrian. New species evolved to fill the niches that they left. Another major extinction occurred 440 million years ago, and yet another 365 million years ago.
Explore the text links to the lower right for more geological and climate information.