"This 4,000-kilometer [2,500-mile] journey now stands as the longest uninterrupted maritime voyage in human prehistory," he said.
The find also coincides with a "pulse of migration into southeast Polynesia about 900 A.D.," Collerson added.
The traditions tell of voyagers pausing before setting out on their epic voyages at a headland on the westernmost tip of Kaho'olawe—a place called Lae o Kealaikahiki, meaning "cape or headland of the way to Tahiti."
The ratio of thorium and uranium to lead in a core sample of C7727 left "a very distinctive isotopic fingerprint of the source region," which confirmed that the tool could only have come from a few sites along the coast of Kaho'olawe.
One such site lies very close Lae o Kealaikahiki, suggesting that sailors may have collected the rocks immediately prior to departure as ballast for their canoes. The stones were probably turned into tools or given as gifts or mementos to distant trading partners later.
The Tuamotu group was likely a center of trade, Collerson added. "It was probably the Singapore of the Pacific."
His study appears in this week's issue of the journal Science.
Voyages No Accident
Ben Finney, a professor emeritus of anthropology at the University of Hawaii, welcomed the findings as further evidence that early Polynesian voyages were far from accidental, as past academics often claimed.
Rather, the journeys were carefully planned and skillfully conducted, he said, with a thorough understanding of the geography of island archipelagoes.
In 1976 Finney and a Polynesian crew sailed a traditional twin-hulled canoe from Hawaii to Tahiti and back "as proof of a concept."
The team used traditional navigation techniques on the journey, such as consulting star and wind compasses, watching migrating birds, and maintaining a bearing relative to prevailing sea swells.
Such voyages would initially have been exploratory, and canoes would have been laden with tools, provisions, and a crew of men and women carefully selected to establish new colonies, Finney said.
The journeys would have been meticulously timed to exploit favorable trade winds, which would have eased return journeys.
"I'm delighted that [Collerson and Weisler] are at last getting some hard evidence for us," Finney said. "We can now get a handle on back-and-forth voyaging."
The challenge now lies in determining the true extent of Polynesian colonization, Finney added.
"Now that we've found a chicken bone in South America, the job is to find those adzes."
Lead study author Collerson agreed, saying the analysis technique has "opened up a Pandora's box of opportunities. We can now track down [the source of stone artifacts] throughout Polynesia."
But further mysteries about the Polynesians remain, he added. While navigational knowledge would have grown as it passed down through hundreds of generations, voyaging in the southeastern Pacific mysteriously ended around A.D. 1450.
"Perhaps that knowledge was lost," Collerson said, "or climate change influenced weather patterns that made sailing more difficult."
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