Florida's peninsula has risen 164 feet during the last 1.5 million years, a University of Florida geologist has calculated. In other words, had sea levels been the same then as now, nearly all of the peninsula would have been under water.

Florida is rising because it is behaving like a tanker pumping out its oil and riding higher in the water. Florida is getting lighter because its bedrock is slowly dissolving and being washed into the ocean.

This makes Florida rise because every part of the Earth's solid crust floats on a subterranean sea of partly molten rock, or magma. Sea floors, made of dense basalt, ride low in the magma sea. Continents, made largely of less-dense granite, ride higher. Florida, unlike most of the continent, is made of unusually porous limestone reefs formed by the skeletons of marine animals many millions of years ago. As such, it is unusually vulnerable to dissolving as rainwater permeates the limestone and washes it into the ocean.

Geologist Neil D. Opdyke said he developed this interpretation of Florida's behavior to explain why fossils of marine animals exist in land deposits in northern Florida that are today as much as 160 feet above sea level.

Other land surfaces have long been known to be rising for different reasons. Maine and Scandinavia, for example, are rising ponderously, rebounding from the extra weight of Ice Age glaciers that have only recently -- in geological terms -- been removed.