Geology of Minnesota

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The geology of Minnesota began 2.7 billion years ago, when the first pieces of volcanic rock that would later form the U.S. state of Minnesota began to rise up out of an ancient ocean.<ref name="Compass">Breining, Greg (December 2005). Compass American Guides: Minnesota, 3rd Edition, 3rd, Compass American Guides. ISBN 1-4000-1484-0.</ref> Much of the underlying gneiss rock of today's state had already been formed nearly a billion years earlier, but still laid underneath the sea. Except for the region where the islands appeared in what is now the northern part of the state, most of the region remained underwater. About two billion years ago, much of the water had drained away. Heavy mineral deposits containing iron collected on the shores of a receding sea to form the Mesabi, Cuyuna, Vermilion, and Gunflint iron ranges from the center of the state up into what is now Canada. These regions also showed the first signs of life as algae grew in the shallow waters.

1.1 billion years ago, a rift valley began to pull the state apart. Lava emerged from cracks along the edges. The rift extended from the current Lake Superior area through the state and down into what is now Kansas. However, the separation stopped before the land could become two separate continents. About 100 million years later, the last volcano in the area went quiet.

550 million years ago, the area found itself repeatedly inundated with water of a shallow sea that grew and receded through several cycles. At this point, the land mass of what is now North America ran along the equator. At that time, Minnesota had a tropical climate. Small marine creatures such as trilobites, coral, and snails float through the sea. The shells of the tiny animals sink to the bottom of the sea, eventually forming limestone and sandstone. When dinosaurs roamed the planet, Minnesota didn't have a remarkable population of thunder lizards. The region remained coastline for a long period, with creatures resembling crocodiles and sharks sliding through the nearby seas. Other land animals followed as the dinosaurs disappeared, but much of the historical record of this time was etched away as glaciers expanded and retreated across the region through several cycles starting about 2 million years ago.

[edit] First human inhabitants

Ice ages come and go as humans develop in other parts of the world. The ice continued to retreat for the last time about 12,500 years before the present time. Melting glaciers filled the lakes and rivers of the state. Minnesota was on the southern edge of Lake Agassiz at this time, a massive lake with a volume rivaling that of the Great Lakes combined together. The River Warren was the southern outlet of the lake, and had an immense flow through the valleys now used by the Minnesota River and Mississippi River. Falls on the river were precursors to the Saint Anthony Falls.

At this time, a number of giant animals roamed the area. Beavers were the size of bears, and mammoths were 14 feet (4.3m) high at the shoulder and weighed 10 tons. Even buffalo were much larger than they are today. Glaciers continued to retreat and the climate became warmer in the next few millennia. The giant creatures eventually died out about 9,000 years ago.