By Paul Rincon
BBC News Online science staff
People in North America were voyaging by sea some 8,000 years ago, boosting a theory that some of the continent's first settlers arrived there by boat.
The tools could have been used for boat-building
That is the claim of archaeologists who have found evidence of ancient seafaring along the Californian coast.
The traditional view holds that the first Americans were trekkers from Siberia who crossed a land bridge into Alaska during the last Ice Age.
The report in American Antiquity makes arrival by boat seem more plausible.
Researchers conducted an archaeological analysis of 9,000-8,000-year-old tools unearthed at Eel Point on San Clemente, one of the eight Channel Islands that lie off the Californian coast.
They propose that some tools used by the prehistoric people of Eel Point may have had the same functions as implements employed for boat-building by Chumash Indians in the early 20th Century.
For example, a triangular "reamer" tool from Eel Point closely resembles a Chumash "canoe drill" used to expand an existing hole in a wood plank.
On this basis, archaeologists Mark Raab, Jim Cassidy and Nina Kononenko argue that the inhabitants of Eel Point were accomplished seafarers.
Animal remains uncovered at the site show that the inhabitants hunted dolphins, sea lions and seals and collected mussels.
Furthermore, Professor Raab points out that the nearby island of San Miguel was occupied by humans 12,200 years ago - circumstantial evidence that sea travel began even earlier.
"The only food resources on the Channel Islands effectively come from the sea. Living there means an intensively maritime way of life," the California State University scientist told BBC News Online.
"People had settled San Nicolas island, about 60 miles from the nearest landfall, between 8,000 to 8,500 years ago. Clearly people were getting around in some kind of watercraft."
Eel Point has a long history of occupation by humans
But some researchers reject suggestions that early Americans colonised the continent by coasting along its shoreline in boats.
They maintain that the first Americans were the Clovis people, who crossed into the New World from Asia when a fall in sea levels at the height of the last Ice Age created a land bridge, known as Beringia, between the two continents.
Lack of evidence
The problem for those backing the coastal migration theory has always been a lack of evidence.
"The basic problem is that all boats are made out of organic materials that just don't preserve in the archaeological record," said Professor Knut Fladmark, of Simon Fraser University in Canada.
Professor Fladmark believes humans were building boats 40,000-50,000 years ago and cites evidence that Australia was colonised by this time despite the fact there was no land bridge connecting it to South East Asia.
"Until you find the boats there will remain a cadre of archaeologists who will insist on not accepting this," Professor Fladmark told BBC News Online.
"Sea level rise since the last Ice Age flooded much of the coastline of North America, presumably drowning any possible evidence of early coastal migrations," Prof Raab added.