by damp wood and burning fitfully, the fire lights the recesses
of the rock shelter where a group of people wrapped in furs huddles
for warmth. Outside, a freezing rain falls. They are on the southern
edge of an immense glacier, in what today is Wisconsin. The glacial
sheet also grips much of Minnesota and Michigan, but it is melting,
and the rivers roar with chunks of ice and debris.
The glacierís demise shapes everything they will encounter
in the time to come. The Midwest is a work in progress, scoured by small
continents of ice, flooded by runoff that fills gorges and depressions.
The region is at the mercy of a fluctuating climate, ruled by an ice
cap at the top of the globe. The Great Lakes are mercurial inland seas,
swelling, shrinking, and sculpting the land.