The Great Lakes formed where they did 20,000 years ago thanks to a hotspot that sat under the supercontinent Pangaea 300 million years ago, before North America even existed.
New research finds that the Cape Verde hotspot, which still exists under the island nation in the Central Atlantic Ocean, heated and stretched the crust under the spot that would eventually become the Great Lakes. This process, which happened over tens of millions of years, led to a low spot in the topography of the region, which glaciers later scraped out during the ice age. After the glaciers retreated, their melt filled the lakes, which now hold 21% of the world's fresh water.
