Ancient kauri trees from Northland have revealed, for the first time, precisely when Earth’s last magnetic pole shift happened and its devastating consequences on the environment.
An international study, published today in Science Magazine, used trees that had been preserved in sediments for more than 40,000 years.
From the data, researchers argued in their paper the shift in the climate and atmosphere could explain other evolutionary mysteries, including the sudden appearance of cave art around the world, the extinction of large mammals in Australia and the disappearance of the Neanderthals in Europe.
Cross-sections from several swamp kauri in NIWA’s archives were analysed by a team from the University of New South Wales, South Australian Museum, NIWA and the Waikato University.
Radiocarbon dating, where an age of a living organism can be estimated by examining its levels of a particular radioactive isotope of carbon, was then used to track changes in radiocarbon levels during the magnetic pole reversal.
The data was then charted alongside annual tree ring growth, which acts as an accurate timestamp.
While scientists already knew the magnetic poles temporarily flipped around 41,000 to 42,000 years ago, they didn’t know exactly how it impacted life on Earth, if at all.
But the researchers were able to detail how Earth’s atmosphere changed over this time, with the consequences of this event etched into tree rings.
"The kauri trees are helping us tie together records of environmental change in caves, ice cores and peat bogs around the world," says co-lead Professor Alan Cooper from the South Australian Museum.
Chris Turney, a professor at UNSW and co-lead author of the study, said when Earth’s magnetic poles shifted and broke down, “unfiltered radiation from space ripped apart air particles in Earth’s atmosphere”.
This would have separated electrons and emitted light in a process called ionisation.
"The ionised air ‘fried’ the Ozone layer, triggering a ripple of climate change across the globe,” Turney said.
Cooper said the sharp increase in UV levels, particularly during solar flares, would have sent people to shelter in caves.
"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 research was funded by the Australian Research Council, the Royal Society of New Zealand Marsden Fund, the University of Waikato, NIWA with support from Ngāpuhi iwi and Top Energy, and other international partners.