Florida is a long-lost piece of Africa.
When North America split apart from Africa around 200 million years ago to form the Atlantic Ocean, a little bit of Africa stuck to North America -- the Florida peninsula and an adjacent region of southern Georgia.
Before the two continents began drifting apart, they had collided about 50 million years earlier in an impact that buckled the eastern edge of North America to form the Appalachian Mountains. The southeastern corner of North America then had no peninsula, but when the continents were pushed apart by a rift, part of Africa stuck to North America.
The discovery that Florida was originally part of Africa, by geologists at Cornell University, emerged from a new method of sending shock waves into the ground and measuring their reflection back to seismographs at the surface. The shocks are generated by special trucks that drive to various locations and, in effect, thump the ground.
Although the induced vibrations are much weaker than those of an earthquake, they travel deep into the ground, bounce off the surface of the crust's "deep basement" layer 30 miles below, and return to the surface. A profile of the deep layer revealed a suture line, or joint between two continental plates. The suture line corresponds to a long-known line of unusually low magnetism that runs roughly east and west from the southern coast of Georgia to southern Alabama.
It had been known that if North America were fitted back against Africa, the magnetic anomaly line would match a similar line in west Africa. Discovery of the suture confirms that the crustal plate to the south originated as part of the African plate.