Stone tools and pieces of animal bone from about 16,600 years ago are the earliest evidence yet of human beings in the New World, scientists say.

The objects were found in the western United States. They were recovered from an archeological site called Cooper's Ferry on the Salmon River near the town of Cottonwood, Idaho.

Scientists used radiocarbon dating methods to find out how old these artifacts are.

The scientists say people lived in or passed through the area at a time when ice covered large parts of North America. That period of time is known as Earth's Ice Age. During the period, big mammals like mastodons, saber-toothed cats and camels lived in North America.

Loren Davis is an anthropology professor at Oregon State University. He led the team of scientists working at Cooper's Ferry. A report on the study and their findings was published in Science magazine.

"The Cooper's Ferry site is the earliest radiocarbon-dated archaeological evidence in the America's," Davis said.

The researchers said the artifacts suggest that people first lived in the area between 16,600 and 15,300 years ago and returned to live there many times after that.

The oldest objects include four sharp stone tools, which were used for cutting and scraping. The scientists also found pieces of stone left from making the tools. They also found burnt pieces of wood, rock that had been split by heat from fires as well as particles of animal bone particles and pieces of horses' teeth. Horses were once native to North America but later disappeared.

A long trip around the world

Scientists say humans first appeared in Africa about 300,000 years ago and later spread throughout the world. There has been much scientific debate about when humans first entered the Americas. They are believed to have crossed into North America at a time when Siberia and Alaska were connected by land.

The new findings support the hypothesis that the first human migration into the Americas traveled down the Pacific coast instead of an inland path.

Davis said, "The Columbia River would provide the first Americans their first route to interior lands south of the continental ice sheets." The Columbia is the biggest river flowing into the Pacific Ocean from North America. It might have provided a way for the early migrants to travel into the North American land mass.

The researchers noted details of some of the sharp objects that would have been used for hunting. These artifacts appear similar to those found in northern Japan from a somewhat earlier date.

Davis said, "We hypothesize that this may signal a cultural connection between early peoples who lived around the northern Pacific Rim."

"Traditional technological ideas spread from northeastern Asia into North America at the end of the last glacial period," he added.

I'm Mario Ritter, Jr.

Will Dunham reported this story for the Reuters news agency. Mario Ritter Jr. adapted it for VOA Learning English. George Grow was the editor.

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archeological – adj. related to the study of the life of people in the past

hypothesis – n. an idea or theory that is not proven but leads to further study

route – n. a path to get from one place to another

interior – n. the part of a land area that is away from the coast

glacial – adj. having to do with glaciers, huge areas of thick ice