The geologic history of the Great Lakes region began soon after the consolidation of the planet 4.6 billion years ago (bya). During the very earliest existence as a globe, the outer shell of the Earth cooled becoming solid. This thin shell was bombarded continuously by meteorites quite heavily until around 4.2 bya. The oldest crust preserved to this day developed after 4.2 bya. The now southern portion of the Superior Province in Minnesota developed between 4.2 and 2.5 bya acting as the nucleus for the development of the rest of the Great Lakes region.
The Archean eon time period from 4.0 -2.5 bya, during which the Superior Province developed, shows evidence of radically different crustal conditions than the present. The Great Lakes region records the transition from Archean to modern conditions well, so to understand the history, we have to understand the change in the conditions.
Cooling of the Earth
When the Earth assembled into a planet four and a half billion years ago, it retained a great deal of heat from the enormous gas and dust cloud it came from, and the radio active elements it contained. In the Archean, heat flowed from the Earth at a much higher rate than at present, somewhere on the order of four times higher due to the decay of short lived radioactive elements that have since decayed away.For this heat to escape the Earth it has to either conduct through the crust, like a frying pan handle, or advect in the form of volcanoes spewing out hot rock, similar to water boiling over the edge of a pot. Conduction through the crust is quite inefficient due to the fact that rocks are pretty good insulators. With the average solid crustal thickness of about 20 km during the Archean, its unlikely this was a major mechanism for heat loss, although undoughtedly it was a factor.
Convection is the way the earth's interior gives off most of its heat. A majority of the convection, or volcanic activity, on the earth takes place at oceanic plate spreading centers like the center of the Atlantic. When rocks crystallize forming new oceanic plate, it releases a lot of heat. To facilitate higher heat loss rates, the crust probably had both more total miles of midoceanic ridge spreading centers and faster subduction rates.
Tectonics, Rocks and Time
In terms of the tectonic setting, a majority of the crust was basic oceanic crust, that lacked any sizable sections of light continental blocks. This oceanic crust was being created at spreading centers and was quickly destroyed in subduction zones that were so numerous, and processed so much crust that they left behind only small sections a few hundred kilometers long. With the surface of the earth recirculating over and over it's amazing that any of these small sections still exists. However, there is a lot of missing time yet to be accounted for.The oldest crust found is around 4 billion years old, yet the planet is estimated to be 4.6 bya. This indicates a missing time span as long of 500 million years which is as the Phanerozoic, or from now back to the early Cambrian. Its important to keep in mind these first rocks of are only the oldest found, however, its unlikely that we will find any significantly older.
We find these Archean rocks in small bunches in every continent because they were the nucleus for the growth of continental crust. Onto these rocks accreted younger rocks also developed by subduction zones, and to a lesser extent, mid oceanic ridges, just as the Archean. As mentioned before, the Superior Province in eastern central Canada, and northern Minnesota was the Archean nucleus for North America.