While the Great Lakes region of North America is well known for its importance to shipping between the United States, Canada, and the Atlantic Ocean, it is also the location of an impressive structure in the continent’s bedrock: the Michigan Basin. Formed during the Paleozoic Era (approximately 540–250 million years ago) the Basin looks much like a large bullseye defined by the arrangement of exposed rock layers that all tilt inwards, forming a huge bowl-shaped structure. The outer layers of the Basin include thick deposits of carbonates—rocks containing carbon and oxygen, such as limestone—deposited over millions of years when a shallow sea covered the region. These carbonate rocks are mined throughout the Great Lakes region using large open-pit mines. The largest carbonate mine in the world, Calcite Quarry, appears in this astronaut photograph.
Published Aug 7, 2006
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