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The flip of the Earth’s magnetic poles coupled with a drop in solar activity 42,000 years ago could have generated an apocalyptic environment that may have played a role in major events ranging from the extinction of the megafauna to the end of the Neanderthals. say the researchers.
Earth’s magnetic field acts as a protective shield against harmful cosmic radiation, but when the poles shift, as has happened many times in the past, the protective shield weakens dramatically, leaving the planet exposed to high-energy particles.
A time shift of the poles, known as the Laschamps excursion, occurred 42,000 years ago and lasted about 1,000 years. Previous work found little evidence that the event had a profound impact on the planet, possibly because the focus had not been on the period during which the poles were actually shifting, the researchers say.
Now Scientists say the change, coupled with a period of low solar activity, could have been behind a wide range of climatic and environmental phenomena with dramatic ramifications. “It probably would have seemed like the end of days,” said Professor Chris Turney of the University of New South Wales and a co-author of the study.
The team has collectively dubbed this period “the Adams event,” a nod to Douglas Adams, the author of The Hitchhiker’s Guide to the Galaxy in which 42 was said to be the “answer to the fundamental question of life, the universe and everything”. .
In an article in the journal Science, Turney and his colleagues describe how they carried out radiocarbon analysis of the rings of ancient kauri trees preserved in the northern New Zealand wetlands, some of which were more than 42,000 years old.
This allowed them to track over time the rise in carbon-14 levels in the atmosphere produced by increasing levels of high-energy cosmic radiation reaching Earth during the excursion to Laschamps. As a result, they were able to date atmospheric changes in more detail than was provided by previous records, such as mineral deposits.
They then examined numerous records and materials from around the world, including lake and ice cores, and found that a number of major environmental changes occurred at the same time that carbon-14 levels peaked.
“We see this massive growth of the ice sheet over North America … we see tropical rain belts in the western Pacific changing dramatically at that point, and then also wind belts in the southern ocean and a drying out in Australia,” he said. Turney.
The researchers also used a model to examine how the chemistry of the atmosphere might change if the Earth’s magnetic field were lost and there was a prolonged period of low solar activity, which would have further reduced the Earth’s protection against cosmic radiation. . The ice core records suggest that such drops in solar activity, known as the “great solar minima,” coincided with the excursion to Laschamps.
The results reveal that atmospheric changes could have resulted in large changes in the weather, thunderstorms and widespread colorful auroras.
In addition to environmental changes that potentially accelerate the growth of ice sheets and contribute to the extinction of the Australian megafauna, the team suggests that they could also be related to the appearance of red ocher handprints, the suggestion is that humans They may have used the pigment as a sunscreen against the increased levels of ultraviolet radiation hitting the Earth as a result of ozone depletion.
They also suggest that the increase in the use of caves by our ancestors at this time, as well as the increase in rock art, could be due to the fact that the underground spaces offered refuge from the harsh conditions. The situation may also have fueled competition, potentially contributing to the demise of Neanderthals, Turney said.
Earth’s magnetic field has weakened by about 9% in the last 170 years, and the researchers say there could be another change in the charts. Such a situation could have a dramatic effect, among other things devastating electricity grids and satellite networks.
Richard Horne, head of space, climate and atmosphere for the British Antarctic Survey, who was not involved in the work, said the chemical changes in the upper atmosphere predicted by the study matched what had been measured at the Halley research station in the Antarctica during strong but short-lived events in which energetic particles from the sun were emitted.
But could the environmental effects have been as severe as the team predicted? “Maybe not that extreme, but it gives you pause to think,” Horne said, noting that it was unlikely that Earth’s magnetic field would disappear completely.
However, Dr Anders Svensson from the University of Copenhagen said that the ice cores of Greenland and Antarctica show no evidence of any dramatic climate change that occurred around the time of the Laschamps excursion, but that does not rule out have an impact. “The changes in the ozone layer and the impact of increased ultraviolet radiation on humans is not something that we can confirm or reject from ice cores,” he said.
Chris Stringer, who studies human origins at London’s Natural History Museum, said the work was important. He said the increased use of the caves as shelter was plausible, but the link to an increase in rock art was less compelling because pig paintings were apparently being produced in Sulawesi, Indonesia, long before the Laschamps excursion.
“The authors also establish a link to the physical extinction of Neanderthals around 40,000 years ago and I think it certainly could have contributed to their demise,” he said. “But they survived longer and spread more than just Europe, and we have a very poor determination about the timing of their final disappearance in parts of Asia.”
Dr Richard Staff, a researcher in quaternary geochronology at the University of Glasgow, said the study was exciting and noted that it could lead to further research on the environmental and evolutionary effects of other, larger dramatic drops in the magnetic field strength of Earth further back. on time.
