Geologic Timescale of Southern Illinois
The land that would become the state of Illinois in 1818 has transformed since life began on Earth. We can reconstruct the position and environment of Illinois at different times in history by studying layers of rock and sediment. Geologic formations and the fossil record in Illinois enable us to look back more than 500 million years, but rocks older than 543 million years are between 2000 and 17,000 feet underground.