Humans arrived in the Americas from Asia at least 9,000 years earlier than previously believed, archaeologists have said, citing an analysis of stone tools found in caves in Brazil.
The discovery of stone tools at Serra da Capivara National Park in northeast Brazil last year suggested humans were present on the American land as early as 22,000 years ago, according to the scientists.
The radiocarbon dating of spear points found in the 1920s placed the arrival of big-game hunters across the Bering Strait about 13,000 years ago, forming the basis of when humans were believed to have arrived in the Americas.
"If they're right, and there's a great possibility that they are, that will change everything we know about the settlement of the Americas," Walter Neves, an evolutionary anthropologist at the University of Sao Paulo, told the New York Times.
The National Park, a Unesco World Heritage Site, is itself a testimony to several evidences that have "forced a sweeping re-evaluation of the fundamental traditional theories underpinning the origins of human settlement in the Americas".
Of more than 300 archaeological sites found within the park, the majority consist of rock and wall paintings dating from 50,000-30,000 years ago.
According to Unesco, many of the rock shelters in the Serra da Capivara National Park are decorated with rock paintings, some of which are more than 25,000 years old.
A few archaeologists disregard the stone tools as an evidence of human settlement in the Americas.
The sharp-edged stones may have resulted from falling rocks, and not human handiwork, according to archaeologist Gary Haynes of the University of Nevada.
Stuart Fiedel of Louis Berger Group, an environmental consulting firm in Virginia, said another possibility was that monkeys produced the tools.
However, other archaeologists said the stone tools found at Serra da Capivara and at other sites across South America show degrees of similarity.
"To say monkeys produced the tools is stupid," archaeologist Dr Tom Dillehay said.