Geochemical fingerprinting was used to ascertain the stone tools' origins.(Supplied: Marshall Weisler/University of Queensland)
Early Polynesian sailors criss-crossed the Pacific for hundreds of years, travelling as far as 2,500 kilometres, according to a new chemical analysis of centuries-old stone tools.
The findings suggest there was ongoing, post-colonisation contact between the communities of the eastern Pacific from about AD1300 to the 1600s.
They also add weight to the view that Polynesia was deliberately settled in one of the greatest maritime migrations in human history.
A detailed study of ancient tools from the Southern Cook Islands, published in the US journalProceedings of the National Academy of Sciences,pinpointed the artefacts' age and the geological source of the rocks from which they were made.
Professor Marshall Weisler from the University of Queensland, who led the research, said the tools — stone adzes — were found at the well-dated Tangatatau rock shelter on Mangaia Island.
The shelter was discovered and excavated in 1989 by Professor Patrick Kirch of the University of California at Berkeley.
In the new study, researchers found some of the source material was brought to Mangaia from distant locations including Rurutu Island, 663 kilometres away in the Austral Islands, and Upolu and Tutuila islands in American Samoa, 1,706 kilometres away.
Excavations in progress during 1991 at the Tangatatau rock shelter on Mangaia Island, Southern Cook Islands.(Supplied: Patrick Kirch/University of California, Berkeley)
The farthest extent of the trading network the researchers were able to track was adze material sourced from the northern Marquesas, Eiao Island, 2,415 kilometres away in French Polynesia.
"We've been able to show that after the Tangatatau site was occupied (around mid-1200s AD) there were several hundred years of post-colonisation interaction," Professor Weisler said.
"That really provides very solid evidence that not only was settlement purposeful, people were maintaining interaction [by] sailing to all these distant archipelagos."
Professor Weisler said the stone adze was ubiquitous in most archaeological sites throughout the region.
It was essential in Polynesian societies because it was "indispensable for shaping canoe hulls, bowls and other artefacts, felling trees for forest clearance permitting agricultural expansion, and fashioning planks and posts for house construction".
He said it was "unsurprising" that the connection to the farthest source, Marquesas, was the first to drop out of the interaction network around the early 1400s.
Communities on Samoa and Rurutu (Austral Islands) continued to interact — directly or indirectly — with Mangaia as late as 1445-1587 whereas contact with Upolu continued until as late as 1537-1672.
Adze movements 'just the tip of the iceberg'
"The colonisation of Oceania is the greatest maritime migration in human history and Polynesians were really at the top of the game of voyaging and return voyaging and … bringing all the necessary items to settle and found a new colony," Professor Weisler said.
He said the ownership of an adze from a distant island such as the Marquesas could have been a status symbol. But the adze was probably not the only item of high significance that was traded.
"They were probably not specifically travelling to get adze material. This might be the tip of the iceberg," he said.
"They would be also bringing perishable items, marriage partners … Things that don't preserve archaeologically."
Professor Weisler said the trade indicated the colonies were part of an integrated society.
"You can pose the question, why are people risking life and limb in these voyages, why were they maintaining these links?" he said.
"It speaks to what societies are. Are they purely functional and economic or are there spiritual, social, religious contexts to societies? And the answer is obviously yes."
Interestingly, the study suggests the boundaries between west and east Polynesia may have been more "porous" than previously thought.
"We've previously distinguished on cultural grounds the differences between east and west Polynesia. But what we've shown [here] is we have adze material from Samoa coming over a long period of time which suggests that the boundaries that we have drawn between east and west Polynesia have a little bit of porosity to them."
Professor Weisler said his team developed a new sampling technique to analyse the artefacts, which uses as little as 200 milligrams for geochemical analysis.
He said this technique could now be applied to artefacts from archaeological sites at other Polynesian archipelagos to determine when long-distance voyaging stopped across the region.