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A period of global upheaval 42,000 years ago was the result of a reversal of Earth’s magnetic field, new research shows.
According to the radiocarbon preserved in the rings of ancient trees, several centuries of climate degradation, mass extinctions and even changes in human behavior can be directly related to the last time the Earth’s magnetic field changed polarity.
The research team named the period of the Adams Transition Geomagnetic Event, or Adams Event, after science fiction writer Douglas Adams, who said number 42 was the ultimate response to life, to the universe and to everything.
“For the first time ever, we were able to accurately date the timing and environmental impacts of the last magnetic pole switch,” said Chris Turney, Earth Scientist, University of New South Wales in Australia.
“The discoveries were made possible by ancient New Zealand kauris, which have been preserved in sediments for more than 40,000 years. Using the ancient trees, we were able to measure and date the peak in atmospheric radiocarbon levels caused by the collapse of the Earth’s magnetic field. “
This most recent period of magnetic reversal is known as the Laschamp event, and this is what we call a geomagnetic excursion. It is at this point that the magnetic poles of the planet briefly change places before returning to their original positions. It is one of the best studied earth’s magnetic field events, recorded by ferromagnetic minerals.
It took place about 41,000 years ago and lasted about 800 years. The exact impact of this event on life on the planet, however, was not clear – so when scientists discovered an ancient kauri tree (Agathis australis) in 2019 who had lived during this period, they took the opportunity to find out more.
This is because trees register atmospheric activity in their annual growth rings. In particular, carbon-14, or radiocarbon, can reveal a great deal of information about celestial activity.
Radiocarbon is only present on Earth in trace amounts compared to other natural carbon isotopes. It was formed in the upper atmosphere under the bombardment of cosmic rays from space. When these rays enter the atmosphere, they interact with local nitrogen atoms to trigger a nuclear reaction that produces radiocarbon.
Since cosmic rays are constantly traveling through space, the Earth receives a more or less regular supply of radiocarbon. Therefore, a radiocarbon spike in tree rings tells us that the Earth has been more exposed to radiocarbon during this year.
When the Earth’s magnetic field is weakened, as during the Laschamp event, more cosmic rays enter the atmosphere to produce more radiocarbon. For this reason, scientists had previously been able to verify that the Earth’s magnetic field had weakened to about 28% of its normal strength during this 800-year period.
The kauri tree, however, enabled the research team to study the years leading up to the Laschamp event. They found that the Adams event took place around 42,200 years ago and that the magnetic field was at its weakest point. before the Laschamp event.
“The Earth’s magnetic field fell to just 0-6% strength during the Adams event,” Turney explained. “We had virtually no magnetic field – our shield of cosmic radiation was totally gone.”
During this time, the Sun’s magnetic field has also reportedly weakened several times, as it also underwent a magnetic reversal as part of its regular cycle. These periods see less sunspots and solar flares, but the Sun’s magnetic field also provides Earth with a measure of protection against cosmic rays – so during these solar minima the cosmic ray bombardment would have increased again.
This weakened magnetic field is said to have triggered substantial changes in Earth’s atmospheric ozone, with dramatic consequences, including dramatic electrical storms and auroras, and climate change around the world.
“Unfiltered radiation from space tore up particles of air in Earth’s atmosphere, separating electrons and emitting light – a process called ionization,” Turney said.
“Ionized air has ‘fried’ the ozone layer, triggering a wave of climate change across the world.”
This is consistent with the climatic and environmental changes of this time seen in other documents around the world, such as the mysterious extinction of Australian megafauna.
Oddly enough, it also coincides with some of our earliest rock art on record, which has prompted researchers to speculate that the Adams event could have driven humans inside.
“This sudden change in behavior in very different parts of the world is consistent with an increasing or altered use of caves during the Adams event, potentially as shelter from the increase in ultraviolet B, potentially to harmful levels, during grandolar minima. or solar energy particles, which could also explain an increased use of red ocher sunscreen, ”they wrote in their article.
It’s a bit speculative, of course, but it does suggest that a geomagnetic reversal can be a serious world-changing event. And recent evidence suggests that we are currently on the brink of another.
This, the researchers say, could be absolutely disastrous in the current climate.
“Our atmosphere is already filled with carbon to levels never seen by mankind before. A reversal of the magnetic poles or an extreme change in the activity of the Sun would be accelerators of unprecedented climate change,” said Turney.
“We urgently need to reduce carbon emissions before such a random event happens again.”
The research was published in Science.
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