The prehistory dating game

By SIMON COLLINS

Fewer than 700 years ago, a violent eruption occurred at Mt Tarawera which dropped ash from the Bay of Islands to Hawkes Bay. Scientists who have studied the event say anyone living close to the mountain, or in the path of a devastating flood that swept down the Tarawera River, would have been annihilated.

Yet, apart from a few legends which may refer to an "ancient" eruption of Tarawera, virtually no memory of this catastrophe appears to have been passed down to later generations of Maori.

"One of the things that amazes me is that there seems to be no oral record of the eruption," says Ian Nairn, a Rotorua geologist who has devoted much of his life to studying it.

"That leads me to believe that there were not many people around at the time."

Maori scholar Hirini Moko Mead, who chairs the runanga of the Ngati Awa people centred at Whakatane just a few kilometres away, is not aware of any traditional accounts of the eruption or the flood.

David Lowe, of Waikato University, who has dated the layer of "Kaharoa ash" laid down by the eruption at AD1314, plus or minus 12 years, says it is critical to timing the arrival of people because no human artefacts have yet been found beneath it.

This is not for want of trying by archaeologists such as Auckland University's Professor Doug Sutton. "Sutton has looked at hundreds and hundreds of sites to see if he can find evidence of people beneath that Kaharoa layer," Lowe says. "So far they have eluded him."

Yet Sutton and a minority of scientists do believe they have found evidence, from quite a different source, that people may indeed have lived in Aotearoa/New Zealand for as long as 1400 years - twice the age of the Kaharoa ash.

In May 1997, the National Institute of Water and Atmospheric Research (Niwa) drilled 35m into sediment 2.3km under the sea 110km east of Hawkes Bay. Mike Elliot and other Niwa scientists then analysed fossilised pollen washed into the sediment from onshore vegetation. As expected, they found high levels of pollen from bracken ferns near the top of the sediment and higher levels of tree pollen further down, reflecting widespread burning of forests since people arrived. But surprisingly, the fern pollen levels started rising in between the Kaharoa ash and a lower ash layer laid down by a huge eruption of Lake Taupo in about AD200. Elliot and his colleagues estimated deforestation began at around AD600.

In a paper submitted to the British journal Nature, they wrote: "We conclude that initial Maori environmental impact occurred at least 650 to 850 years earlier than the most widely accepted age for first settlement of New Zealand."

Nature rejected it. So did Earth Science and Planetary Letters. The paper is still unpublished. Elliot believes that is because the anonymous referees who criticised it were among many local scientists who refuse to accept evidence that challenges the orthodox position.

"If I can put it bluntly," he says, "they have published themselves into a corner and they are very unwilling to be objective about it."

When Elliot's post-doctoral fellowship at Niwa ended in 2000, there was no job for him. He says the Institute of Geological and Nuclear Sciences complained that analysing fossilised pollen was its business and Niwa should keep out of it. Unable to earn a living in science, Elliot went teaching. He now teaches geography at Whangarei Boys' High School.

Similar bitter personal disputes have long dogged the study of human origins. In 1996, when Christchurch zoologist Richard Holdaway published a paper in Nature dating the arrival of Pacific rats in New Zealand to around AD100, archaeologist Atholl Anderson withdrew his name from the paper.

"It totally contradicted his published position and he didn't want it to be true," Elliot says.

Anderson, of Ngai Tahu heritage and now director of the Centre for Archaeological Research at the Australian National University, was away on fieldwork this week and did not respond to Herald attempts to contact him.

If the rats, or kiore, really did arrive in AD100, experts agree that they could only have come with humans. A poll of New Zealand archaeologists at their annual conference last April found them equally divided: 27 were inclined to believe Holdaway's evidence; 24 were not. But in the same poll, almost two-thirds of the archaeologists said people did not settle in Aotearoa until after 1100, suggesting that earlier visitors did not stay.

The issue needs to be set in context. On a global scale, the story of human settlement is remarkably recent. The Earth has existed for 4.5 billion years. But homo sapiens is believed to have evolved only about 200,000 years ago, and for about half of the time since then it was confined to Africa.

Around 100,000 years ago, the first humans crossed the Sinai and spread eastwards, probably reaching China and Australia a bit more than 60,000 years ago. Settlement of the Pacific has been traced back to the rise of a group of languages called "Austronesian" (from the Latin for "south" and the Greek for "island"). Today Austronesian speakers stretch from Malaysia to Hawaii, plus an outpost in Madagascar off the coast of Africa.

Austronesian speakers migrated out of Taiwan to the islands of the Philippines and Indonesia about 5300 years ago, spreading southeast past northern New Guinea to the Solomon Islands by about 3600 years ago, interbreeding with the indigenous people and giving present-day Polynesians a genetic inheritance which is a mix of Asian and Melanesian gene types.

From there on, the dates are controversial.

A theory called the "express train to Polynesia", shown on the map, suggests the Austronesian speakers pushed quickly into the islands of "remote Oceania" as far as central Polynesia by 3200 years ago, and Aotearoa 1000 years ago.

Former Auckland University anthropologist Roger Green, who has spent a lifetime studying the Pacific, agrees with the general direction of settlement, but prefers to call it a process of "pause, pulse and step".

In his view, the archaeological evidence shows that people did not reach Fiji, Tonga and Samoa until about 1000 BC, and then "paused" to develop the double-hulled canoe before venturing on, reaching Aotearoa around 1200 to 1300.

By the time of these epic voyages, the experts agree that the Polynesians must have become confident navigators, partly using birds which clustered around every island in huge numbers before human predators arrived.

Recent work by Auckland University biological anthropologist Lisa Matisoo-Smith has found that some ancient rat bones in the North Island are genetically different from the East Polynesian kiore which Maori settlers brought with them in the main migrations, suggesting earlier visitors may have come from further west.

"In the recent past no one has suggested that successful settlement was from anywhere other than Eastern Polynesia. Linguistically, culturally and genetically it all fits," she says. "But we know that people were in the Pacific for 3000 years, so there are people who know the ocean.

"I don't find it difficult to believe that people were visiting here 1000 years before it was settled."

Professor John Flenley, a Massey University geographer, who is organising a symposium on dating initial settlement here at the NZ Geographical Society's annual conference in Auckland in July, believes that Elliot's pollen samples and other evidence also show that some of the visitors did not go home.

"I think they came, but remained in small numbers because, apart from hunting and fishing, they couldn't really get much to eat. Their tropical crops wouldn't grow very well."

He agrees that all the evidence shows a sudden surge in human impacts from about AD 1300.

However, he suggests that this may be because after years of experiments, the Maori worked out how to prepare the poisonous root of the bracken fern so it could be eaten. People would have cleared forests in favour of fern. This "fern revolution" could account for a huge jump in fern pollen counts as people burned forest to make way for bracken.

Most scientists, however, are sceptical. Holdaway, for instance, is certain the early visitors cannot have stayed. For a start, he says, they clearly did not eat the moa, which were so few in numbers and so easy to catch that he believes humans virtually wiped them out within 160 years of settling permanently.

"People say people could be here for 500 years and be invisible [in the archaeological record]. That's just not possible. They would have had to ignore the largest supply of protein on land. No one in their right mind would collect 13,000 mussels if there was another supermarket around."

In a remarkable piece of genetic detective work, Penny and others have calculated the founding population of Aotearoa must have been at least 100 to 200, including at least 50 females, in order to grow to around 100,000 with the amount of genetic diversity existing when Europeans first arrived.

After smaller and smaller groups split off along the 5000-year migration trail from Asia, Maori ended up before European contact with less maternally inherited genetic variability than any other sizeable human group studied so far.

Landcare ecologist Matt McGlone says that if they had been here 1400 years, there would have been time to develop much more diversity. "Everything reeks of them having got here very recently."

In McGlone's view, Elliot's pollen counts from marine sediments are unreliable because the pollen that is washed into the sea is not all from current vegetation.

"It's reworked and reworked," he says.

"Every Cyclone Bola will clean out a bit more of the river bank. What Mike has done is confuse the effect of a major volcanic eruption, the Taupo eruption, that did produce a huge amount of open land dominated by bracken.

"We think that has contaminated the picture he is showing."

Elliot and Flenley, for their part, are confident their data is not contaminated. Elliot intends to submit his paper to another journal this year.

"There are other types of evidence that are lending some support to it, and I think my evidence is going to be corroborated from a rather unusual piece of research."

What kind of research that is, he's not saying. The search for new evidence on our origins is not over yet.