The shifting history of North America's ancient ice sheet
Imagining a vast ice sheet sprawling over Canada and extending down into what is now the northern United States, reaching as far south as Pennsylvania, Ohio, Indiana, Michigan, and Wisconsin, helps us grasp the scope of ancient glacial coverage between 19,000 and 26,000 years ago. Yet, while picturing this immense ice mass is fascinating, the present-day implications of its retreat - parti