Scientists have gained a rare glimpse into a moment 42,000 years ago when Earth’s magnetic field temporarily went out of control, thanks to a perfectly preserved ancient tree fossil. A 2021 study suggests this event led to environmental chaos, possibly influencing everything from increased cave paintings to the extinction of Neanderthals.
Earth’s magnetic field is essential for life, protecting us from harmful solar radiation and keeping our atmosphere intact. However, it is not static—it shifts over time and even flips completely every few hundred thousand years. The last major geomagnetic reversal occurred 780,000 years ago, but smaller disruptions, called geomagnetic excursions, happen more frequently.
The most recent of these, the Laschamps Excursion, occurred around 42,000 years ago, when the magnetic poles temporarily switched before flipping back again 800 years later. “The Laschamps Excursion was the last time the magnetic poles flipped,” explained Chris Turney, co-lead author of the study. “They swapped places for about 800 years before changing their minds and swapping back again.”
Scientists knew these pole shifts happened, but their impact on life and the environment was unclear—until a massive, 42,000-year-old kauri tree was discovered in New Zealand. Found during preparations for a power plant, the tree’s rings provided a 1,700-year record of environmental conditions during the Laschamps Excursion.
“For the first time ever, we have been able to precisely date the timing and environmental impacts of the last magnetic pole switch,” said Turney. “Using the ancient trees, we could measure and date the spike in atmospheric radiocarbon levels caused by the collapse of Earth’s magnetic field.”
Published in Science, the study used radiocarbon data from the tree to create a timeline of atmospheric changes during the Laschamps Excursion. The team then ran climate models incorporating global data to analyze the event’s environmental effects.
A Period of Extreme Change
The study revealed a dramatic period of environmental upheaval, especially in the years leading up to the magnetic field reversal. The findings suggested that a weakened ozone layer, increased UV radiation, and higher atmospheric ionization levels all peaked around 42,000 years ago.
In tribute to author Douglas Adams—who famously wrote in The Hitchhiker’s Guide to the Galaxy that the answer to life, the universe, and everything is “42”—the researchers named this period the “Adams Transitional Geomagnetic Event.”
“The more we looked at the data, the more everything pointed to 42,” said Turney. “It was uncanny.”
The study suggests that during this time, the sky would have been filled with intense auroras and violent electrical storms due to increased ionization in the atmosphere.
“Early humans around the world would have seen amazing auroras, shimmering veils and sheets across the sky,” said Alan Cooper, co-lead author of the study. “It must have seemed like the end of days.”
Could It Have Shaped Human Evolution?
One of the study’s more controversial theories is that the Adams Event influenced human behavior. Researchers suggest that the increase in UV radiation may have driven early humans into caves for shelter, leading to an increase in cave art.
“We think that the sharp increases in UV levels, particularly during solar flares, would suddenly make caves very valuable shelters,” Cooper suggested. “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 study also raises the possibility that the Adams Event contributed to mass extinctions of megafauna in Australia and played a role in the decline of Neanderthals.
Chris Stringer from the Natural History Museum of London acknowledged the study’s importance but cautioned against drawing direct links. “The authors also make a link with the physical extinction of the Neanderthals around 40,000 years ago, and I think it could certainly have contributed to their demise,” he said. “But they did survive longer and ranged more widely than just Europe, and we have a very poor fix on the timing of their final disappearance across swathes of Asia.”
Could It Happen Again?
The study raises concerns about whether a similar event could happen today. Cooper pointed out that Earth’s north magnetic pole has been shifting rapidly, moving across the Northern Hemisphere.
“This speed—alongside the weakening of Earth’s magnetic field by around nine per cent in the past 170 years—could indicate an upcoming reversal,” Cooper warned. “If a similar event happened today, the consequences would be huge for modern society. Incoming cosmic radiation would destroy our electric power grids and satellite networks.”
The study, published in Science, provides new insights into Earth’s magnetic history and its potential effects on life—past, present, and future.
Source: UNSW
