Searching the Seabed for Florida’s Ice Age Societies

Five miles off Florida’s coast, in a sandy pit on the seafloor near a coral reef, archaeologist Morgan Smith picked up a stone tool someone dropped on dry land 7,000 years ago.

It was December 2024, and Smith, an associate professor of anthropology at the University of Tennessee at Chattanooga, was diving on an underwater mission to find signs of ancient human life. He sifted through 30 inches of sand and crushed seashells, down to a layer of blue-gray clay silt that could only have formed in a terrestrial environment.

There, in this ancient, submerged dirt, he found a stone scraping tool the size of his hand. Digging deeper, he and one of his students also found an 8,500-year-old hunk of wood from a prehistoric tree.

“Holy cow!” Smith recalls thinking. It was the first time anyone had found a stone tool buried in ancient dirt beneath this part of the ocean.

Today, this spot is eight feet underwater. But millennia ago, after the last Ice Age, modern-day Florida’s western coastline extended around 100 miles further out. That’s the coastal landscape the first human beings in North America would have found when they arrived at least 15,000 years ago in what is today the coastal region of the southeastern U.S. Since then, sea levels have risen more than 300 feet.

That now submerged land now holds clues about the lives of America’s earliest residents. With 100 miles of their former homelands now underwater, Ian Thompson, an archaeologist and the tribal historic preservation officer for the Choctaw Nation, thinks there are “significant early archaeological sites” throughout the region.

Today, Thompson and Smith are among nearly a dozen scientists working on a new five-year project funded by the federal Marine Minerals Administration (MMA) to survey the seabed and find better ways to identify archaeological sites hidden beneath it. They hope their work will make it easier for researchers to piece together a picture of what life in this lost landscape looked like.

“Thirty years ago, the challenge was: Can we find these sites?” said Jessica Cook Hale, an underwater archaeologist at Britain’s University of Bradford’s Submerged Landscapes Research Centre. “Now, the question is: What were people doing there?”

The answer could change our understanding of how ancient humans survived the globe-spanning floods that followed the last Ice Age and even how and when people first came to the Americas. “These sites,” notes Sara Dailey-Smith, a partner on the MMA project representing the Chickasaw Nation, “could be lost pages of our history.”

The MMA project is the biggest effort in history to identify where people might have lived across the 89 million submerged acres, from Texas to western Florida, that were once land. But the scientists are building on decades of research done by pioneering divers who have been searching for archaeological sites here since 1989.

The team behind this work has spent the past two years analyzing sonar scans of the seafloor and sub-bottom profiles made using sound waves that show buried layers of sediment and rock. Combining data from academic archives and oil and gas companies, they’re making a map of a drowned world.

“We’re looking for large features on the landscape people would have been drawn to in the past,” said Melanie Damour, a marine archaeologist at MMA.

Scans revealed a web of ancient river channels carved into the underwater bedrock. Where modern rivers meet the sea, these ghostly channels continue for miles offshore, showing scientists where fresh water once flowed.

For archaeologists, these ancient river channels have been fruitful locations to look for ancient sites.

Thousands of years ago, people could have fished these waters or hunted animals that stopped by for a drink. Some channels run past deposits of flint, chert, or other stone that people used to make tools, which may have made them irresistible stops for hunter-gatherers.

“You might as well put up a Walmart sign on one corner and a Home Depot sign on the other,” said Andy Hemmings, an archaeologist at the Aucilla Research Institute in Florida.

The Aucilla River, about an hour south of Tallahassee, has been a gold mine for underwater archaeologists brave enough to descend into its dark water alongside hidden alligators and water moccasins.

In a sinkhole 30 feet beneath the river surface, researchers exploring the region in 2016 found a stone knife and mastodon bones that showed signs of human butchery from around 14,500 years ago—which helped prove that people arrived in North America centuries earlier than scientists previously thought. And in 1981, amateur divers swimming through a nearby tributary found the skull of an extinct bison with a broken spear point sticking out of its forehead, 10,500 years after a hunter apparently dealt it a death blow.

Following the Aucilla and other nearby rivers offshore, archaeologists have excavated about 25 additional sites, including a 5,000-year-old shell midden built from burned oysters on a bygone coast, rock quarries littered with discarded tools, and the sandy pit where Smith dug up the stone scraper and the hunk of wood.

But the rest of the ancient coastline is largely unexplored. Scientists believe there are thousands of sites left to find.

“Even though there are more people doing this work than ever before, we still know comparatively nothing about what’s out there,” said Smith.

This summer, MMA scientists and tribal partners also began surveying the seafloor off the east coast of Texas, following the Trinity River offshore to an area where they believe people may have lived and the geological conditions are right for preserving soil and artifacts.

If scans of the seafloor support the scientists’ hunch, they’ll return to collect sediment cores to confirm their suspicions. From the back of a boat, they’ll push long tubes into the seabed to get a cross-section of the buried layers of sand, shell, and—they hope—long-forgotten soil. If they get lucky, they might pull up a tool or a stone flake created by humans chipping away at stone.

“But that’s like hitting the lottery,” said Damour, the MMA archaeologist, with a yearning in her voice that only a scientist could summon for an old rock chip.

By documenting ancient history, MMA aims to keep archaeological sites from being damaged if companies build offshore oil and gas rigs or wind turbines nearby.

“You can’t protect what you can’t detect,” said Damour.

The scientists hope their work will also help future archaeologists find more sites and answer big questions about American history: When and how did people come to this continent? What were their lives like? How did they survive massive sea-level rise?

“There are questions we can’t answer at terrestrial sites,” said Cook Hale. “There are traces of lifeways, cultural adaptations, human responses to climates, and ecologies we have no analog for today that can only be found on the continental shelf.”

Archaeologists debate, for instance, whether the first people to migrate to the Americas walked across the Bering Land Bridge in Alaska or landed boats somewhere along America’s coasts. Evidence of human settlements along now-submerged coastlines could help settle this debate by showing where humans migrated and when. So far, scientists have found vanishingly few traces of early coastal residents.

That hasn’t deterred Hemmings of the Aucilla Research Institute. In 2009, he followed the channel of the Suwannee River 125 miles off the coast of northern Florida to a spot he and his colleagues nicknamed Thor’s Elbow. Hemmings dove 130 feet and planted his flippers on the old riverbank where, he mused, “it’s unlikely anyone else had stood for 11,000 years.”

At such an extreme depth, he could only stay for nine minutes, so he planted some equipment on the seabed and planned to return to take sediment cores. But a tropical storm scrapped the return visit, and the team never got funding for another expedition. Thor’s Elbow and other potential deepwater sites they identified remain out of reach.

“It’s driving me crazy,” he said. One day, he hopes some combination of divers and underwater drones will thoroughly study the sites.

Thompson, the Choctaw historical preservation officer, said he hopes future research will uncover more evidence about how life changed for ancestors of the Choctaw and other tribal nations in the southeast during a period of dramatic environmental changes.

“They tended to concentrate in river valleys, which were low areas that are susceptible to sea level rise,” he said.

After the Ice Age, rising seas swallowed land and lifted the water table, reconfiguring rivers and springs and transforming inland areas from forests to wetlands. During the quickest bursts of glacial melting, around 14,000 years ago, people adapted to oceans rising about a foot per decade.

“If you were born on the coast, by the time you were 25 you would have had to pick up your whole village and move it 300 or 600 feet inland,” said Neil Puckett, lead principal investigator at the private archaeological firm SEARCH.

Today, seas are rising an inch or two per decade, but modern cities won’t be so easy to move. The changes ancient people lived through should be a modern-day warning, said Dailey-Smith of the Chickasaw Nation.

“We have to learn from this,” she said. “The experiences of past peoples give us perspective, resilience, and practical lessons for responding to the environmental challenges we face today.”

To uncover more of that history, the University of Tennessee’s Smith is already planning a return trip with his students to the stretch of seafloor where he pulled a stone tool out of ancient soil. There are deeper sediment layers to excavate that could reveal even older artifacts, he says. “There's definitely something waiting down there for us to go back to.”