Some changes are global and some changes are local.
Scientists have learned that the Earth's crust is a thin, solidified layer of rock floating on a largely molten interior. The crust is broken into a number of plates that slowly slide on the surface. Although the movement is only centimeters a year, over millions of years continents have moved thousands of kilometers. The positions of the continents affect climate on local and global levels.
Before Europeans settled here, two-thirds of Illinois was covered by a tallgrass prairie - a diverse plant community with hundreds of species. Today, the Illinois prairie has been converted to urban and agricultural areas dominated by a few species. Only small remnants of the original prairie remain.