by Kevin Theissen
Our planet is a dynamic, ever-changing system and this past Saturday at the market we explored the fascinating science of geology with a team of students and faculty from the University of St. Thomas. Geologists use physical models to understand the natural behavior of streams like our local Mississippi River. The models provide insight on major processes such as erosion, transport, and deposition–and the sometimes hazardous consequences which include flooding and landslides. Visitors got hands-on experience investigating the interactions between water flow and landscape with a table-top stream table. They created hills, dams, slopes, and stream channels and experimented with changes in the rate of streamflow. Visitors learned that the “sediment” for our stream table was an unexpected material—recycled toilet seats!
The Earth’s large crustal plates move at the rate that our fingernails grow and accordingly lead to much slower changes than rivers. Given hundreds of millions of years, however, those slow changes mean dramatic differences. Visitors observed marine fossils of organisms known as brachiopods, bryozoans, and crinoids representing a shallow tropical sea that once covered the Twin Cities and much of southeastern Minnesota during a period of geologic time known as the Ordivician, more than 450 million years ago. Reconstructions of plate movements suggest that Minnesota was likely centered on the equator during this time.
Visitors also donned 3-D glasses to get dramatic views of a variety of important plate tectonic settings where plates converge, spread apart, and slide past each other. Perhaps the best example of this is the Pacific ‘Ring of Fire’ which includes deep-sea trenches, mid-ocean ridges, and several large mountain chains.
Junior scientists topped all of this off by decorating their own pet rocks!