Scientists have made a huge discovery of mastodon bones that could totally change how scientists think about the southeastern United States.

Researchers found stone tools and mastodon bones at the bottom of a river in Florida that suggests that humans lived there 14,550 years ago, about 1,500 years earlier than had been though, according to a Florida State University statement.

The discovery was made in the Aucilla River, and was reproted in the journal Science Avances.

The study lasted four years and involved having divers explore a hole 30 feet underwater in the river, excavating artifacts such as a mastodon’s tusk and a knife fragment. Scientists think this indicates that hunter-gatherers along with dog companions butchers a mastodon carcass at the edge of a sinkhole. Rising sea levels have since turned the area into a river.

“This is a big deal,” Florida State University Assistant Professor of Anthropology Jessi Halligan said in the statement. “There were people here. So how did they live? This has opened up a whole new line of inquiry for us as scientists as we try to understand the settlement of the Americas.”

The statement added that researchers used the latest radiocarbon dating techniques to find these artifacts. Scientists had previously thought a group of people called Clovis had settled the area 13,200 years ago.

“The new discoveries at Page-Ladson show that people were living in the Gulf Coast area much earlier than believed,” said Michael Waters, director of Texas A&M’s Center for the Study of the First Americans.

Added Halligan: “It’s pretty exciting. We thought we knew the answers to how and when we got here, but now the story is changing.”