Ancient people lived on small islands in the Everglades, according to recent research -- and the trash they left behind is helping solve the mystery of how the islands came to be.
As scientists chisel through hard layers of rock and dig up piles of ancient and buried waste materials, they are finding evidence of settlement, abandonment and resettlement in the area, beginning more than 5,000 years ago -- thousands of years earlier than experts originally thought.
But the settlers didn't just live on the islands, the evidence suggests. They may have also helped create their habitable enclaves.
By piling up mounds of fish remains, turtle bones and other waste products, these people probably altered the chemistry of the soil and raised the elevation of the islands, making the land even more welcoming to all kinds of life.
Together, accumulating studies on the area's geology and archaeology may ultimately help preserve a unique and threatened ecosystem. The work also offers insights into a long history of complex interactions between people and the environment.
"This is just one of a number of cases where people and human disturbances played a major role in landscape development," said McGill paleoecologist Gail Chmura, who presented some of the latest findings this week at the American Geophysical Union's Chapman Conference on Climates, Past Landscapes, and Civilizations. "This landscape is now cherished. That's one major human-nature interaction lesson there."
Throughout the swampy Everglades, hundreds of elevated, tear-shaped islands form havens for trees, vegetation and wildlife. The islands also present a curious set of mysteries.
Raised just a meter or two above the water line, all of the islands are fixed in place, Chmura said. They are all oriented in the same direction. And they all have a high point in the same place. Based on those patterns, scientists have long suspected that people somehow influenced their formation.
Evidence for that theory first came in 2005, when archaeologist Margo Schwadron began excavating on some of the islands and found 42 archaeological sites that were full of human garbage. These trash mounds, or middens, contained ceramics, seeds and lots of animal bones, among other types of domestic debris.
The oldest scraps dated back more than 5,000 years, which blew away previous estimates that people first settled the Everglades just 500 to 1,000 years ago. Except for a period of yet-to-be explained abandonment between 4,400 and 2,700 years ago, the area remained populated for millennia.
"That is the new discovery, and it changes everything," Schwadron said. "All the models thought this was an uninhabitable swamp, and who would ever live there? This demonstrates that people were there from day one, and they lived there continuously for thousands of years."
It now also seems likely that the islands benefitted from their inhabitants. Fires, food waste and other refuse would have built up, forming raised areas of land for occupation by plants, animals and people. As the waste dissolved and broke down, discarded bones in particular would have helped create productive, phosphorous-rich soil.
No one can say for sure whether this process of landscape development was intentional or accidental.