Trees allow us to have a glimpse into the past, as their rings reveal so many things about the climate in a given year. An examination of these rings can show if the winter was wet that year, if there were any hurricanes or forest fires, and so on.
In Ngawha, on New Zealand’s North Island, people discovered an ancient tree that contains a record of a reversal of Earth’s magnetic field. The tree—an Agathis australis, also known as its Māori name kauri—was found during excavation work for the expansion of a geothermal power plant.
Ngāwhā Generation, which is a subsidiary of Northland power wholesaler Top Energy, gave the kauri tree back to iwi on the agreement scientists could take samples for study.
The tree has been buried in 26 feet of soil, and measures eight feet in diameter and 65 feet in length. Carbon dating indicated that it lived for 1,500 years, between 41,000 and 42,500 years ago.
Alan Hogg, from New Zealand’s University of Waikato, explained:
“There’s nothing like this anywhere in the world. This Ngāwhā kauri is unique.”
The lifespan of the kauri tree covers a point in the history of the Earth when the magnetic field almost reversed. The magnetic north and south went on an excursion but did not quite complete a full reversal.
It is believed that the Earth’s magnetic field is generated by the iron in the planet’s core. It produces electric currents that extend far into space as it moves around. The magnetic field is actually like a barrier that protects the planet from the solar wind. This is a stream of charged particles from the Sun that could strip away the ozone layer if it were to affect the atmosphere.
When the magnetic field reverses, it weakens and causes more radiation from the Sun getting through. Scientists have previously associated extinction events with magnetic field reversals.
The rings of this kauri tree have a complete record of a near-reversal, so this is the first time a tree that lived during the entire event has ever been found.
“It’s the time it takes for this movement to occur that is the critical thing…We will map these changes much more accurately using the tree rings.”
The kauri tree unearthed during the expansion of the Ngāwhā Generation geothermal power plant.
Scientists now analyze the samples of the tree and are led by Chris Turney from the University of New South Wales, an expert in paleoclimatology and climate change over the past 40,000 years. The research is being funded by the Australia Research Council.
Scientists hope to get an insight into what we should expect the next time it happens.
“We will have increased cosmic radiation. It will take out satellites and it might take out other communication infrastructure.”
“The precious thing is this huge, lonely tree grew for some 1700 years across a remarkable period in our planet’s history when the Earth’s magnetic field flipped some 42,000 years ago, a period known as the Laschamp Excursion. Funded by the Australian Research Council we’re undertaking detailed measurements of the radioactive form of carbon through the tree rings.”
Over the past 83 million years, there have been 183 magnetic pole reversals.
This process takes about 7,000 years to complete. Monika Korte, the scientific director of the Niemegk Geomagnetic Observatory at GFZ Potsdam in Germany, says:
“It’s not a sudden flip, but a slow process, during which the field strength becomes weak, very probably the field becomes more complex and might show more than two poles for a while, and then builds up in strength and [aligns] in the opposite direction.”
According to NASA, magnetic field reversals occur at random intervals, even though in the last 20 million years, it appears to have settled into a pattern, happening once every 200,000 to 300,000 years.
The last full reversal happened around 780,000 years ago.
Recently, scientists announced that the magnetic north pole had moved unexpectedly.
Instead of tracking steadily from the Canadian Arctic towards Siberia, it sped up so much that researchers had to update the World Magnetic Model (WMM), which is a representation of Earth’s magnetic field. It is used extensively in navigation by the U.S. Department of Defense, the U.K. Ministry of Defense and many civilian systems—so knowing exactly where the northern and southern magnetic poles are is of utmost importance.
“Because the Earth’s magnetic field has a major effect on how much radiocarbon carbon is formed in the upper atmosphere, these precious analyses will allow us to investigate the magnitude and rate of change when the magnetic field reversed during the Laschamp; something not possible before and of great interest given recent changes in the Earth’s magnetic field. ”