An ancient tree that contains a record of a reversal of Earth’s magnetic field has been discovered in New Zealand. The tree—an Agathis australis, better known as its Māori name kauri—was found in Ngawha, on New Zealand’s North Island, during excavation work for the expansion of a geothermal power plant, stuff.nz reports.
The tree, which had been buried in 26 feet of soil, measures eight feet in diameter and 65 feet in length. Carbon dating revealed it lived for 1,500 years, between 41,000 and 42,500 years ago.
“There’s nothing like this anywhere in the world,” Alan Hogg, from New Zealand’s University of Waikato, told the website. “This Ngāwhā kauri is unique.”
The lifespan of the kauri tree covers a point in Earth’s history when the magnetic field almost reversed. At this time, the magnetic north and south went on an excursion but did not quite complete a full reversal.
Earth’s magnetic field is thought to be generated by the iron in the planet’s core. As it moves around, it produces electric currents that extend far into space. The magnetic field acts as a barrier, protecting Earth 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 impact the atmosphere.
When the magnetic field reverses—or attempts to—it gets weaker, leading to more radiation from the Sun getting through. Previously, scientists have linked extinction events to magnetic field reversals.
The newly discovered kauri tree’s rings contain a complete record of a near-reversal—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,” Hogg told stuff. nz.
Samples of the tree are now being analyzed by scientists, led by Chris Turney from the University of New South Wales—an expert in paleoclimatology and climate change. Understanding what happened to the tree during the event could provide 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,” Hogg said.
Turney told Newsweek: “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.”
Magnetic field reversals happen at random intervals, although in the last 20 millions years it appears to have settled into a pattern, happening once every 200,000 to 300,000 years, NASA says. The last full reversal took place around 780,000 years ago.
Scientists recently announced 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)—a representation of Earth’s magnetic field that is used by GPS systems worldwide.
“Because the Earth’s magentic 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,” Turney said.