Scientists diving in a Florida river found bones and tools that could change the history of humans in the Americas.

These new items -- called artifacts -- could mean humans lived in the Americas more than a thousand years earlier than was known before.

Researchers from several universities worked together and published their findings in the journal Science Advances.

The items were found in the underwater archeological site called Page-Ladsen. Long ago it was a watering hole where people and long-extinct animals lived. Today it is part of the Aucilla River in Florida.

It has provided scientists with human and animal artifacts for more than 50 years.

Researchers used carbon dating -- a scientific method -- to find out the age of the objects. Previous carbon-dated items brought up from the waters were between 11,000 and 13,000 years old.

But a newer find? It is more than 14,000 years old.

Jessi Halligan teaches anthropology at Florida State University. She says the older artifacts change the way researchers will study human history in the Americas. She says these buried items were found in an untouched part of the river. That means there is no question about their age.

"So we've got to reexamine everything we thought we knew, so it's kind of opened up this whole new world of first Americans studies."

Halligan says they found a cutting tool — a stone knife — buried underwater. The stone was formed into a tool that only a human could make.

This made the researchers take a second look at a mastodon bone brought up from the same water hole in the river. It had been cut. Mastodons were large ancient animals that once lived on Earth, but died off thousands of years ago.

Halligan says there was "no way that the marks on it were made by a natural process." In other words, those marks on the mastodon bone? "They were made by people," she says, people who used tools to kill and cut up the animal.

"When we went back, what we found was a stone tool that could not have been made by nature, that was definitely cultural, that dated to 14,550 years ago."

But who were these people who made the tool and killed and ate the mastodon?

Until this discovery, researchers thought the first Americans were a group they call "Clovis" hunters.

They were a prehistoric Indian culture thought to be the most ancient people in North America. They came to North America from Asia when glaciers melted, and they could walk across land that formed a bridge between the continents.

Now, science puts this newly found Florida tool at more than a thousand years before the Clovis hunters. Halligan says it is significant, or important, that the tool is made by human hands.

"Now that's significant, A) because the site shows people were definitely here before Clovis, more, about 1,500 years before Clovis, but B) because it shows that people had to have come to the Americas by a different route than we had accepted. Because, the ice-free corridor that supposedly people came from by land through Canada, was not open 'til 14,000 years ago."

There had been some evidence that humans were in the area earlier than the Clovis hunters. But until now, nothing had been proven because so few older remains had been found.

Scientists said it is possible changing sea levels could be the reason more evidence had not been found about these ancient Americans before now.

Halligan told reporters that 14,000 years ago, sea levels were 100 meters lower than today -- because of glaciers.

Over time those large areas of ice melted. And the evidence of the ancient humans in the Americas was lost. Evidence ended up buried and underwater -- making it much harder to find.

The evidence also shows a much different world than the one today. There were camels and mastodons and giant armadillo-like animals living there. But they all died, or went extinct, 10,000 or 11,000 years ago.

One other interesting discovery — the researchers think they found bones from dogs. Even back then, they were likely to have been trained to help humans.

Now it will be the job of researchers to try to find new artifacts.

I'm Anne Ball.

Kevin Enochs reported on this story for VOANews. Anne Ball wrote this story for Learning English. Kathleen Struck was the editor.

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artifact – n. a simple object made by people in the past

archeological – adj. having to do with the science of past human life and activities by studying the bones, tools, etc. of ancient people

extinct – adj. no longer existing

prehistoric – adj. relating to the time before people could write

glacier – n. a very large area of ice that moves slowly down a slope or valley or over a wide area of land

armadillo - n. an animal with a hard shell covering its body