Glacial Beginnings
Welcome to the Ice Age, for we may be in the midst of one now. Fortunately, if we are, we are still within an interglacial period, an ice-free break when the glaciers are in retreat toward the poles. But, the glaciers may come again.
There have been at least four different Ice advances in the Cenozoic Era/Quaternary Period. We are currently about 12,000 years into an interglacial period of the Plesitocene Ice Age which began two million years ago. Within each Ice Age, there are periods of glaciation (lasting 60,000 to 90,000 years) and warmer, interglacial times (lasting 10,000 to 40,000 years.) These cycles are based on the sun.
The most recent glacial advance -- called the Wisconsinan, began its advance across North America 20,000 years ago. Its march across our land destroyed whatever earlier glaciers may have done to our landscape, so our story of the glacial Great Lakes starts here.