Paleontology and geology
The Precambrian: The earliest history of Wisconsin is recorded by rocks over two billion years old. Some of these rocks represent the deposits of ancient seas, volcanoes, and underground bodies of magma. Though these rocks provide evidence of the physical environment, they do not contain fossils, thus we have no record of the organisms from the Precambrian.
The Paleozoic: Warm, shallow seas covered much of the state during the early to middle Paleozoic (Cambrian – Devonian). These seas have left behind an extensive record of marine life, including brachiopods, bryozoans, trilobites, corals, bivalves, gastropods, cephalopods, sponges, crinoids, and the scales and teeth of early fishes and sharks. Fossils of rare soft-bodied animals have been found in Cambrian sediments in the central part of the state. The record of the later Paleozoic (Carboniferous – Permian) is missing due to erosion that followed an interval of gentle uplift.
The Mesozoic: Wisconsin continued to lie above sea level throughout the Mesozoic. Erosion outpaced deposition, thus there are no known rocks or fossils from this era in the state.
The Cenozoic: There are no Tertiary rocks in Wisconsin, as most of the state was above sea level and exposed to erosion. During the Quaternary, massive ice sheets covered most of the state. The classic glacial landforms in the state are so striking that the final North American ice advances are named the Wisconsinan. Animals adapted to a cold climate, such as the wooly mammoth, large beavers, and horses, inhabited Wisconsin’s spruce and hemlock forests. Fossils of seal, walrus, and whale are found along the Great Lakes.