A massive swamp kauri log unearthed near Kaikohe is around 40,500 years old and could shed new light on a mysterious global event which may have dramatically influenced the Earth's climate.

The log, which is 16m long and weighs 60 tonnes, was found during excavation for a new geothermal power station near Ngāwhā Springs.

It was delivered to Ngāwhā Marae on Wednesday by power company Top Energy in a major logistical operation.

During the formal welcome and blessing, Top Energy chief executive Russell Shaw told the hapū, Ngati Rangi, it didn't feel like a gift.

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''It feels like it's being returned to its rightful owners,'' he said.

The 28-tonne stump is lifted from its resting place at the Ngawha power station construction site, with the trunk already loaded on a transporter. Photo / Debbie Beadle
The 28-tonne stump is lifted from its resting place at the Ngawha power station construction site, with the trunk already loaded on a transporter. Photo / Debbie Beadle

Project site manager Mike Ohs said the tree was found preserved in clay 9m underground during site works for the new power station.

Sections about 1.5m long had to be cut off either end so it could be moved. The stump alone weighed 28 tonnes.

The three sections were lifted by crane then trucked about 5km along State Highway 12.

The operation started about 8am on Wednesday with the tree on the marae grounds by noon.

Ngāwhā Marae Trustees Komiti chairman Richard Woodman said no decision had been made yet about what to do with the rawa (resource).

Carving was one possibility but there was a lot of talking to be done first.

It's a tight fit as a transporter carrying the log turns into the marae entrance from State Highway 12. Photo / Debbie Beadle
It's a tight fit as a transporter carrying the log turns into the marae entrance from State Highway 12. Photo / Debbie Beadle

The marae was open to sharing the rakau (tree) if other marae wanted some of it, and he was aware other hapū had questioned why it had been given to Ngāti Rangi.

''We definitely know that we're not just going to keep it for ourselves,'' he said.

Woodman said it was a ''fantastic acknowledgement'' from Shaw that the tree was being returned rather than gifted.

The find has also sparked great excitement among scientists hoping to gain a better understanding of the ancient climate.

Alan Hogg, director of the Waikato Radiocarbon Dating Laboratory at Waikato University, dated the tree to 40,500 years plus or minus 400 years.

That made it of great interest to scientists studying the Laschamp Event, a ''magnetic reversal'' in which the Earth's north and south magnetic poles switched places.

It was not known exactly when the reversal occurred but it was thought to have been about 41,000 years ago.

Studying the level of radioactive carbon-14 in the Ngāwhā kauri's rings would allow scientists to pinpoint more accurately when the reversal occurred and for how long.

Until now no tree had been found anywhere covering this later period of the reversal, Hogg said.

Taikaha Baker, 4, of Waimate North, gives the ancient kauri a hongi. Photo / Debbie Beadle
Taikaha Baker, 4, of Waimate North, gives the ancient kauri a hongi. Photo / Debbie Beadle

One of the reasons scientists were interested in magnetic reversals — and the accompanying drop in the Earth's magnetic field strength, which allowed more solar radiation to reach the Earth's surface — was that they could have a major effect on climate.

''So this tree is critical, we've never found one of this age before. We're very excited, and incredibly grateful to Ngāwhā Marae for allowing us to take samples.''

Going by its size the tree was likely to have been 1500-2000 years old when it died, Hogg said.

Despite the scale of the excavations at Ngāwhā — about 900,000cu m in total — Shaw said only one tree had been uncovered so far.

The company had also consulted the Northland Regional Council and the Ministry for Primary Industries about the find.

The tree found at Ngāwhā was part of a vast kauri forest which cloaked the upper North Island before the arrival of humans. Deforestation accelerated rapidly around 1820 after the arrival of Europeans. It is estimated that only 4 per cent of the original forest remains.

Top Energy's relationship with Ngāti Rangi had developed during the consenting process for the power station, Shaw said.

Ngāwhā Marae members and guests line up for a photo with the 40,000-year-old tree. Photo / Debbie Beadle
Ngāwhā Marae members and guests line up for a photo with the 40,000-year-old tree. Photo / Debbie Beadle

Earthworks for the new power station started in 2017 and are due to be completed in July.

When the 28MW power plant is built, scheduled for late 2020, it will more than double the Far North's energy production to 53MW.

If a third power plant is built as planned, output will reach 81MW, making the Far North a net energy exporter.