North America

The eastern coast of North America was once part of an ancient "Ring of Fire" surrounding an ocean that has disappeared forever from Earth. From Greenland to Georgia, and through the Gulf coast states into Mexico, the collision of continents raised mountains comparable to the Himalayas and Alps of today. Several ranges were raised up on the eastern border of North America between 480-230 million years ago.

The Taconic mountains rose 480 million years ago, wrinkled under pressure like the hood of a wrecked car, from Maryland to the Gaspe Peninsula of Quebec. The compressed rocks from this mountain-building event are exposed in the Taconic Range of New York, and in eastern Pennsylvania. But by 410 million years ago the peaks that had towered over the east coast had been eroded away, and the sea washed over their exposed roots and covered them with level deposits of limestone. As these mountains wore down, the resulting sediment filled a shallow sea basin running from New York southward to Alabama, in layers up to 1,000 ft (300 m) thick.

Another collision about 450 million years ago created the Acadian mountain range, whose roots are exposed today in Newfoundland. These mountains began to be torn down by rain and wind, and by the time they had worn down to nothing, more than 63,000 cubic miles of sediment made from them had been dumped into the shallow continental sea between New York and Virginia-about the same amount of rock as the Sierra Nevada mountains of today. The bones of amphibians, the first land animals, are found in the rocks laid down by the streams of East Greenland.

The sleepless crust under North America's Pennsylvanian-age borders tossed and turned in complex ways. Three hundred million years ago, North America sat on the equator, its vast inland sea surrounded by rain forests whose fossilized remains are the coal deposits of the eastern United States. Small mountain ranges rose out of the sea that covered the center of the continent in Colorado, Oklahoma, and Texas. The Ouachitas stood in the Gulf coast states, the last great mountain range to stand there. In the eastern United States, the Allegheny mountain range stood where the Acadian and Taconic ranges had stood before.

The Ouachitas welded South America to the Gulf coast, at roughly the same time as the Alleghenies welded the East coast of North America to West Africa. The Ouachitas and Alleghenies stretched, unbroken, all the way around the eastern and southern coasts of North America. This joining of the world's continents formed Pangaea, the most recent supercontinent in geologic history. Pangaea's 150 million year history ended with the birth of the Atlantic Ocean and the separation of North and South America. As South America and Africa tore away from North America, Florida was left behind, attached to the intersection of the Allegheny and Ouachita mountains. Another legacy of this cracking of Earth's crust is the New Madrid fault, which runs through the North American Plate under the Mississippi valley.