
Almost 20,000 years ago, Earth's climate began to warm. Because of the changing temperatures, a miles-thick ice sheet started to shift. As the ice sheet moved, it carved deep pits in the land and left water in its wake. This melted ice filled the new cavities. This is the story...

Almost 20,000 years ago, Earth's climate began to warm. Because of the changing temperatures, a miles-thick ice sheet started to shift. As the ice sheet moved, it carved deep pits in the land and left water in its wake. This melted ice filled the new cavities. This is the story...