Northland kauri tree study might have revealed what killed off the Neanderthals

The importance of preserving kauri has perhaps never been clearer. 

Scientists looking at ancient kauri trees in Northland say they've come across evidence within them that could rewrite human history. 

"It's the most surprising and important discovery I've ever been involved in," said Professor Alan Cooper of the South Australian Museum, who co-led the new research, published Friday in journal Science.

So what exactly did they find? Evidence that about 42,000 years ago the Earth's magnetic pole went haywire, perhaps wiping out the Neanderthals, but sending Homo sapiens into the safety of caves and inspiring art that we're still finding today. 

While the approximate date of the pole shift was already known, examination of the kauri has allowed scientists to "precisely date the timing and environmental impacts of the last magnetic pole switch", according to Chris Turney, professor at the University of New South Wales.

They've dubbed it the 'Adams Event', after author Douglas Adams, whose book The Hitchhiker's Guide to the Galaxy famously said the answer to the 'Ultimate Question of Life, the Universe, and Everything' was simple '42', without specifying the question. 

"The findings were made possible with ancient New Zealand kauri trees, which have been preserved in sediments for over 40,000 years," said Turney. "Using the ancient trees we could measure, and date, the spike in atmospheric radiocarbon (the radioactive isotope or type of carbon) levels caused by the collapse of Earth's magnetic field."

Until now, what impact the shift of the poles may have had on life hasn't been clear. 

Firstly, as the poles switched places the Earth's magnetic field virtually disappeared.

"Earth's magnetic field dropped to only 0-6 percent strength during the Adams Event," said Turney. "We essentially had no magnetic field at all - our cosmic radiation shield was totally gone."

This is bad, and coincides with the extinction of the Neanderthal people and megafauna across Australia.

But it also would have produced spectacular aurora in the skies, far from the poles where they can be seen now, and wild electrical storms.

"Unfiltered radiation from space ripped apart air particles in Earth's atmosphere, separating electrons and emitting light - a process called ionisation," said Turney. 

"The ionised air 'fried' the ozone layer, triggering a ripple of climate change across the globe."

Early Homo sapiens - that's us - might have fled into caves for shelter, then inspired by what they were seeing outside, start to paint.

"We think that the sharp increases in UV levels, particularly during solar flares, would suddenly make caves very valuable shelters," said Dr Cooper. "The common cave art motif of red ochre handprints may signal it was being used as sunscreen, a technique still used today by some groups."

The trunk found in Ngāwhā. Photo credit: NIWA

Dr Cooper told NPR people would "not want to be outside during daylight hours" during the Adams Event, which lasted a few hundred years before the poles switched back to where they were, and still are to this day.

One tree in particular was very useful - a massive kauri with a 2.5m-wide trunk found in Ngāwhā that lived through the Adams Event.

"Like other entombed kauri logs, the wood of the Ngāwhā tree is so well preserved that the bark is still attached," said Jonathan Palmer, a specialist in dating tree rings at the University of New South Wales.

In the last 83 million years, the magnetic poles have swapped places 183 times. The Adams Event of about 42,000 years ago - also known as the Laschamp event, after lava flows in France where evidence of the swap was first discovered in the 1960s, is the most recent. 

"The more we looked at the data, the more everything pointed to 42," says Turney. "It was uncanny. "Douglas Adams was clearly on to something, after all."

Kauri alive today are at risk from dieback, a disease first discovered in 2006. There's still no cure for it. Native to New Zealand, the species only exists in the upper North Island.

The magnetic north pole has shown considerable movement in recent years, speeding away from Canada - where it spent most of the past few centuries - towards Russia.