Editing Illinois (section)

===Geology===
{{Main|Geology of Illinois}}

During the early part of the [[Paleozoic Era]], the area that would one day become Illinois was submerged beneath a shallow sea and located near the Equator. Diverse marine life lived at this time, including [[trilobite]]s, [[brachiopod]]s, and [[crinoid]]s. Changing environmental conditions led to the formation of large [[Coal forest|coal swamps]] in the [[Carboniferous]].

Illinois was above sea level for at least part of the [[Mesozoic]], but by its end was again submerged by the [[Western Interior Seaway]]. This receded by the [[Eocene|Eocene Epoch]].

During the [[Pleistocene Epoch]], vast ice sheets covered much of Illinois, with only the [[Driftless Area]] remaining exposed. These [[glacier]]s carved the basin of [[Lake Michigan]] and left behind traces of ancient glacial lakes and [[moraine]]s.<ref>{{Cite journal |last1=Willman |first1=Harold Bowen |last2=Atherton |first2=Elwood |last3=Buschbach |first3=T. C. |last4=Collinson |first4=Charles William |last5=Frye |first5=John Chapman |last6=Hopkins |first6=M. E. |last7=Lineback |first7=Jerry Alvin |last8=Simon |first8=Jack A. |date=1975 |title=Handbook of Illinois stratigraphy |journal=Bulletin - Illinois State Geological Survey |volume=95 |location=Urbana, IL |url=https://www.ideals.illinois.edu/handle/2142/35115 |access-date=November 26, 2020 |archive-date=August 20, 2019 |archive-url=https://web.archive.org/web/20190820230836/https://www.ideals.illinois.edu/handle/2142/35115 |url-status=live }}</ref>