2. 40 million years later, Florida and northwest Africa separated as the Central Atlantic Ocean formed.

6. These layers formed a platform, an area of continent that is composed of flat-lying layers of sedimentary rock.

9. At that time, the Appalachian Mountains north of Florida began to erode very rapidly.

11. Florida During the Ice Ages Over the last 1.8 million years, parts of the Florida Platform emerged and disappeared beneath the sea several times.

13. During interglacial periods, sea level rose and water covered much of the Florida Platform.

16. Corals established themselves in the shallow sea along the edge of the Florida Platform.

18. When sea level dropped, these reefs were exposed. They form the present-day upper Florida Keys.

19. The lower Florida Keys formed as sand accumulated behind the reef, covered it, and eventually emerged from beneath the ocean.