Great Lakes
Scientists seek clues to the formation of North America's Great Lakes, the largest expanse of fresh water on the planet; delving into an underground salt mine; investigating a fossilized coral reef; diving to the bottom of Lake Superior.
Scientists seek clues to the formation of North America's Great Lakes, the largest expanse of fresh water on the planet; delving into an underground salt mine; investigating a fossilized coral reef; diving to the bottom of Lake Superior.