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The shift of the Earth’s magnetic poles with a decline in solar activity 42,000 years ago could have generated an apocalyptic environment that could have played a role in major events ranging from the extinction of the megafauna to the end of the Neanderthals. , according to the researchers.
Earth’s magnetic field acts as a protective shield against harmful cosmic radiation, but when the poles switch, as has happened several times in the past, the protective shield weakens considerably and leaves the planet exposed to particles of high energy.
A temporary pole reversal, known as the Laschamps excursion, occurred 42,000 years ago and lasted approximately 1,000 years. Previous work has found little evidence that the event had a profound impact on the planet, possibly because the focus had not been on the period in which the poles were actually moving, the researchers said.
Now Scientists say that the turnaround, associated with a period of low solar activity, could have been at the origin of a wide range of climatic and environmental phenomena with dramatic ramifications. “It probably would have seemed the end of days,” said Professor Chris Turney of the University of New South Wales and co-author of the study.
The team collectively called this period the “Adams Event,” a nod to Douglas Adams, author of The Hitchhiker’s Guide to the Galaxy in which 42 was seen as the “answer to the question.” ultimate of life, of the universe and of everything ”. .
In the journal Science, Turney and his colleagues describe how they performed radiocarbon analyzes of ancient kauri rings preserved in the wetlands of northern New Zealand, some of which were over 42,000 years old.
This allowed them to track over time the increase in carbon-14 levels in the atmosphere produced by increasing levels of high-energy cosmic radiation reaching Earth during the Laschamps excursion. As a result, they were able to date atmospheric changes in more detail than those offered by previous documents, such as mineral deposits.
They then examined numerous documents and materials from around the world, including lake and ice cores, and found that a host of major environmental changes were occurring as carbon-14 levels peaked.
“We see this massive ice cap growth over North America … we see the tropical rain belts in the western Pacific shifting dramatically at this point, then also the wind belts in the southern ocean and a drying out in Australia, ”Turney said.
The researchers also used a model to examine how the chemistry of the atmosphere might change if Earth’s magnetic field was lost and there was an extended period of low solar activity, which would have further reduced Earth’s protection against cosmic radiation. Ice core records suggest that such declines in solar activity, known as “great solar minima”, coincided with the Laschamps excursion.
The results reveal that changes in the atmosphere could have led to huge changes in climate, electrical storms and extensive colored auroras.
Aside from the environmental changes that may accelerate the growth of ice caps and contribute to the extinction of Australian megafauna, the team suggests that they could also be linked to the emergence of red ocher handprints, the suggestion being that humans may have used the pigment as a sunscreen against the increased levels of ultraviolet radiation hitting the Earth due to ozone depletion.
They also suggest that the increase in the use of caves by our ancestors during this time, as well as the rise of rock art, could be due to the underground spaces providing shelter from the harsh conditions. The situation may also have spurred competition, potentially contributing to the end of Neanderthals, Turney said.
Earth’s magnetic field has weakened by about 9% over the past 170 years, and researchers say another flip could be considered. Such a situation could have a dramatic effect, in particular by devastating electricity grids and satellite networks.
Richard Horne, head of space, weather and atmosphere at the British Antarctic Survey, who was not involved in the work, said the chemical changes in the upper atmosphere predicted by the study corresponded to what had been measured at the Halley Research Station in Antarctica during strong but short-lived events in which energetic particles were emitted from the sun.
But could the environmental effects have been as severe as the team predicted? “Maybe not as extreme, but it gives you pause to think,” Horne said, noting that Earth’s magnetic field was unlikely to disappear completely.
Dr Anders Svensson of the University of Copenhagen, however, said ice cores from Greenland and Antarctica show no evidence of dramatic climate change around the time of the Laschamps excursion, but this does not exclude that it has an impact. “The changes in the ozone layer and the impact of increased UV radiation on humans is not something that we can confirm or reject with ice cores,” he said.
Chris Stringer, who studies human origins at the Natural History Museum in London, said the work was important. He said the increased use of caves as shelter was plausible, but the link to an increase in rock art was less convincing as paintings of pigs were apparently produced in Sulawesi in Indonesia long before the Laschamps excursion.
“The authors also make a connection with the physical extinction of the Neanderthals around 40,000 years ago and I think that certainly could have contributed to their demise,” he said. “But they have survived longer and spread more widely than Europe alone, and we have a very bad idea of when they finally disappeared in parts of Asia.”
Dr Richard Staff, a quaternary geochronology researcher at the University of Glasgow said the study was exciting and noted that it could lead to further investigation into the environmental and evolutionary effects of other larger dramatic declines in the strength of the Earth’s magnetic field further back. on time.
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