As part of the continent Gondwana 650 million years ago, the foundation of Florida was tucked between the land masses that would become South America and Africa. The rest of eastern North America was then part of another continent called Laurentia. As the Earth’s tectonic plates shifted, the basement rocks of our modern continents moved across the globe.
About 300 million years ago, Gondwana and Laurentia collided, forming the Appalachian Mountains in what would become North America and the Mauritanide Mountains in what would eventually be Africa. The Florida portion of Gondwana joined with Laurentia at a line that runs southwest to northeast through modern south Alabama, south Georgia, southern South Carolina, and eastern North Carolina.
By about 200 million years ago, Gondwana and Laurentia had sutured together to form the supercontinent Pangea. At this point Florida’s basement rock was located north of the equator, much closer to its current position, but was surrounded by land. Florida was near the middle of the Pangea supercontinent, far from any ocean, probably surrounded by desert. Pangea did not last long from a geological perspective, breaking up after just 85 million years.
The breakup of Pangea resulted in the creation of Florida as a peninsula.
“North America separated from Africa, South America separated from Africa, Europe and Asia did their own thing, India broke away and slammed into the south side of Asia, creating the Himalaya mountains,” says Albert C. Hine, professor of Marine Science at the University of South Florida and author of the book “Geologic History of Florida: Major Events That Formed the Sunshine State.”
“So it was a period of time where there was a significant reorganization of the continental masses on earth, and during that time the basement rocks that created the Florida peninsula were isolated and left alone, and then on top of the basement rocks, the limestones have accumulated that we see, and the rocks and sediments that we see that form our beaches have occurred over the past 200 million years,” Hine says.
For tens of millions of years, most of Florida was separated from the rest of North America by the Georgia Channel Seaway. Eventually, the water receded and Florida became a visible extension of North America, but with a distinctly different foundation than the rest of the continent. The Suwannee Basin and the Florida-Bahama Blocks that make up the foundation of the Florida peninsula have much more in common with the rocks of northwest Africa than with the bedrock of the rest of North America.
At different points in geologic history, Florida has been totally submerged, but it has also been twice as wide as it is now.
“During glacial events, the huge ice sheet, it’s called the Laurentide Ice Sheet, covered most of North America, and the Fenno-Scandanavian Ice Sheet covered most of Europe,” says Hine. “Water was extracted from the ocean and snowed on land. Over thousands of years, that snow built up into thick ice sheets. So water was withdrawn from the ocean as much as 400 feet. So sea level dropped about 400 feet, 130 meters. As a result, Florida being topographically low and flat, that exposed a huge portion of the Florida platform to the air, and became dry.”
Prehistoric animals and probably Pre-Columbian people lived on dry land that is now submerged under 200 feet of water in the Gulf of Mexico.
Hine says that rising sea levels are an inevitable part of Florida’s future.
“It’s a function of global warming and global climate change,” says Hine. “Scientists realize, of course, it’s been politicized, to our chagrin, but the data are real, and the predictive models are the best we can possibly make them, and they’re getting better with time. That’s been demonstrated. All that clearly shows that sea level is going to rise in Florida in time periods that are important to humans. Not thousands of years or millions of years, but in decades. As a result, we have to start to plan how we’re going to deal with that. As we’re planning, we continue to try to make the science better, and to make the predictions better.”