Paleontology and geology
The long complex history of the Precambrian is intermittently recorded in Minnesota and includes evidence of the early formation of the North American continent, as well as times of mountain building and erosion. Volcanic islands formed during the Precambrian of Minnesota, followed by the deposition of unusual sedimentary layers called banded iron formations (BIFs). These BIFs are evidence of microbial life in the Precambrian sea. Other sedimentary structures formed by the activity of bacteria, such as stromatolites, are also common in Precambrian rocks. These fossils are typically primitive, single-celled organisms.