Hundreds of thousands of years ago when sea level was higher than its present level, the Upper Keys were a living coral reef. As sea level fluctuated over time, coral reefs have been alternately submerged and exposed, allowing the coral polyps, the small animals that build the reef, to create large structures. When sea level dropped, the coral was exposed forming the islands of the Florida Keys. Over time, the island was colonized by plants from the Bahamas, Caribbean and West Indies as seeds were transported by wind, sea and in the intestinal tract of migrating birds, most notably the white-crowned pigeon. The tropical hardwood hammock that thrives on this island was once common on the highest elevations in the Upper Keys. In 1919, William J. Matheson, a wealthy Miami chemist, bought this 280-acre island and built a caretaker's home with a windmill for electricity and a cistern for rainwater.