Fossil hunters uncover Florida's geologic history listen11/04/10 Matthew Cimitile
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Florida’s history didn’t begin with Ponce de Leon, the founding of St. Augustine, Hernando de Soto or even the indigenous Calusa people. Clubs around Florida are venturing out to rock quarries, phosphate mines and river beds to uncover ancient fossils and get a glimpse into Florida’s geologic past.
Kneeling on the limestone surface at Vulcan quarry mine in Brooksville, Shirley Gissy of Port Richey, Florida and a member of the Tampa Bay Fossil Club, takes her rock hammer and meticulously chisels out a piece of Florida’s geologic history.
"I’ve always enjoy being outdoors and it’s an adventure, you never know what you are going to find out here. We found a lot of echinoids and clams and bones and we just enjoy being outside. We really enjoy finding the fossils; it tells us something about what this was like millions of years ago. This was under water and finding sand dollars down here and sea urchins, that is a quest, they are hard to find but it is always exciting.”
Many groups like the Tampa Bay Fossil Club explore terrain such as rock and phosphate mines and riverbeds to uncover ancient marine and land animals that populated Florida and created the limestone we live on. At Vulcan Construction Materials rock quarry, the quarrying process allows fossil hunters to excavate terrain more than 50 feet below the surface and millions of years back in time. Alan Pagels is Vulcan’s Safety, Health and Environmental Coordinator who helps direct the hunts at the rock quarry.
“This area we are in right now is called the Brooksville Ridge. If you look at a topographical map you will notice that this area gets up to 200 to maybe in some areas 300 feet above sea level. Basically, we are in a pit, been digging in here anywhere from 60 to 80 feet down from the surface. We are at an elevation right now of about 20 feet above sea level and we are finding a bed out here of sand dollars, quite a variety of sea urchins and other burrowing type of sea life that was out here.”
Fred Hendershot, the Tampa Bay Fossil Club’s field trip director, said that marine fossils of clams and sand dollars from the Oligocene, a period stretching back roughly 24 to 33 million years ago, are common at the quarry and tell of Florida’s geologically recent emergence from the water.
“Florida wasn’t even here until it started coming out of the ocean about 30 million years ago. One of the things I ask when I go to a 4th grade or 5th grade class is how many dinosaurs lived in Florida? I get all kind of answers from 10 to 10 thousands. The answer is none because Florida wasn’t here, the dinosaurs all went extinct 65 million years ago and there was no Florida until 30 million years ago.”
Once it emerged from the ocean due to the accumulation of eroded sediments from the north and skeletons of billions of small marine creatures, Florida experienced numerous advances and retreats of the sea. Joshua Slattery, a doctoral student in the department of geology at the University of South Florida, said the presence of marine fossils 20 miles from the shore tells the story of a land that encountered considerable sea-level fluctuations though time.
“Florida is kind of like a dipstick basically and it records how sea level has changed over millions of years. It is not affected by tectonic activity like mountain building events at all, so you can actually see how the sea has changed through time. It fluctuates and wherever you are in time you can figure out how the seas were and you can recreate the paleogeography. Various factors but the primary has been the amount of glacial ice. Basically as climate has changed over the last 40 million years, temperature became much more cooler. As temperatures became more cooler, more water became trapped in polar ice caps and also in mountain glaciers, and as they got trapped in there sea levels would begin to drop. Occasionally, we would go through fluctuations where the amount of ice at the poles would decrease or increase, and as they decreased or increased sea levels would rise or fall over millions of years, so you would have periods where Florida was completely submerged and then other times where Florida was mostly land.”
According to the Florida Geological Survey, during the last ice age that began 100,000 years ago, glaciers that covered Canada and the northern U.S. sucked up so much water that Florida’s Gulf of Mexico coastline was 75 to 100 miles further west than today. While during much warmer, peak interglacial periods, thermal expansion and glacial melting caused sea levels to rise considerably and submerge much of the state.
Hendershot said that the fossil club also uncovers the remains of unique and massive land species like mammoths, saber-tooth tigers, giant ground sloth and mastodons that lived as recently as 10,000 years ago.
“Most of your big mammals were in the 5 million range and more recent. Most of the phosphate mines and places that we go to in Arcadia, Wauchula, down in that area of Florida, its 5 million to 1 million, even as recent as 10,000 years. There were elephants walking literally right here, 10,000 years ago. We have seen places where men had killed the elephant and chopped it up with his spears and stuff. We know that man overlapped with some of the bigger animals at the time.”
According to the Florida Museum of Natural History, shortly after Florida’s first people arrived about 12,000 years ago, most of the giant mammals quickly died out. Experts blame the extinctions on a combination of over-hunting and climate change. Scientists think such climatic and human activity is causing a more severe extinction globally today.