In the 1950s a new method of archaeological analysis, radiocarbon dating, allowed organic materials such as wood, shell or bone to be accurately dated. All living organisms contain a radioactive form of carbon (carbon-14), which decays at a known rate. Therefore, by measuring the amount of carbon-14 a once-living object retains, scientists can determine its age. While the radiocarbon dating method can provide close estimations of age, the figures should not be regarded as exact.
From the 1960s to the 1980s the oldest radiocarbon dates derived from analysis of settlement sites in New Zealand were 1000–1100 CE or even a little earlier. During the 1990s these dates were systematically re-assessed as the technique became better understood, and many problems were found with earlier dates. For example, it was realised that radiocarbon dates obtained from charcoal fragments were often unreliable: the wood could have come from a tree that was hundreds of years old when it was burnt, and so an occupation site would seem much older than it really was. As a result, the reliable dates all belong to the period after 1250.
Analysis of volcanic ash
Ash that has erupted from volcanoes, consisting of volcanic glass, rock fragments and mineral grains, has a distinct chemical makeup. This means it can be analysed to identify and date when eruptions occurred. Ash fallout from the volcanic eruptions at Taupō (known as the Taupō ash) in 232 (± 15 years), and at Tarawera (known as the Kaharoa ash) in 1314 (± 12 years), might have buried existing settlements. In the eastern North Island, archaeological remains of Polynesian occupation have been found immediately above the Kaharoa ash layer. This settlement must have occurred after that eruption. But no similar remains from beneath either the Taupō or the Kaharoa ash layer have yet been uncovered.
Some theories about a settlement date around 1300 are based on environmental factors. From East Polynesia, New Zealand lies in a southerly direction and in a different weather system. The prevailing winds make it difficult to sail non-stop in a straight line from East Polynesia to New Zealand, or from New Zealand to East Polynesia. By dating archaeological evidence of people stopping over at islands on their return journey, it is possible to suggest the date when they might have reached New Zealand.
The teeth may tell
The Wairau Bar in Marlborough is one of the oldest known archaeological sites in New Zealand. Researchers Tom Higham, Atholl Anderson and Chris Jacomb, who have radiocarbon-dated it at 1288–1300, suggest that some of the oldest burials there could include people born in tropical Polynesia. Science could provide a way to test this idea. A person’s diet in Polynesia is likely to have differed markedly from that at Wairau Bar. By looking at trace elements in teeth and bones, scientists could possibly tell what a person’s diet was likely to have been, and perhaps where they lived. Recently, similar research in Europe used the oxygen content of tooth enamel to conclude that a person buried in England in 2300 BC was actually born in the European Alps.
The Kermadec group and Norfolk Island lie about halfway between East Polynesia and New Zealand, and it is likely that Polynesian explorers returning from New Zealand stopped at these islands on the way. Distinctive New Zealand obsidian, a glassy volcanic rock used for cutting, is found in archaeological sites on the Kermadecs, and may have been carried there by returning voyagers. Radiocarbon dates of archaeological sites could support the theory that New Zealand and its northern satellite islands were settled at about the same time.
Settlement of the Chatham Islands
Radiocarbon dates for the settlement of the Chatham Islands are currently later than for mainland New Zealand – around 1500. This is consistent with the stages of cautious Pacific exploration: first the Kermadecs, then New Zealand (possibly including as far south as Enderby Island in the subantarctic Auckland Islands), then the Chathams.