It is attracting attention as a result of a study showing that mankind’s art work called murals in caves was due to dramatic changes in the Earth’s magnetic field. Changes in the Earth’s magnetic field are so destructive that it has created extreme weather, which it is argued is related to the extinction of large mammals in Australia and Neanderthals in Europe.
Currently, the Earth’s magnetic field flows out of the magnetic pole and flows through the magnetic pole. However, the direction may be reversed, and a magnetic field may flow from the magnetic north pole to the magnetic south pole. This is called geomagnetic reversal. Geomagnetic reversal occurred once in 200,000 to 300,000 years, and the last time it occurred is about 780,000 years ago.
Ancient kauri trees found in New Zealand contain surprising clues about the reversal of Earth’s magnetic field. ©Nelson Parker
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However, there was a phenomenon in which the direction of the Earth’s magnetic field was not completely reversed, and after a short period of time away from the normal state, it returned to its original state. This is called’geomagnetic excursion’, and it happened about 42,000 years ago.
Geology calls this the’Laschamps event’ because the traces were found in the lava flow of a small village called Laschamps in France.
Even modern science cannot predict when these events will occur and how they will specifically affect the Earth when they occur. However, an ancient kauri tree found in New Zealand had surprising clues about it.
Ancient kauri tree discovered by accident during excavation
The kauri tree was found in Nguhua, north of Auckland, New Zealand. While excavating on a hillside to build a geothermal power plant, a kauri tree, 20m long, 2.4m wide, and 65t in weight, was accidentally discovered in February 2019.
The kauri tree, a type of Mesozoic coniferous tree, is the largest and longest living tree in the world. Therefore, the tree rings contain information about the climate of the atmosphere at the time. This kauri tree, which sprouted about 42,715 years ago, was preserved enough to have green leaves after it was buried in a coal bed that had not been completely carbonized after living about 1600 years.
Alan Cooper from the Museum of South Australia, Chris Turney from the University of New South Wales in Australia, Norbert Nowakzyk from the German Geological Research Center (GFZ), and Florian Adolfi from the Alfred Wegener Institute analyzed the tree rings. They found that the change in radioactive carbon-14 in the atmosphere was exactly the same as the Lachamp event.
The researchers analyzed the tree’s rings and found that the change in radiocarbon-14 in the atmosphere was exactly the same as the Lachamp event. ©Kate Evans (Alan-Hoggs-lab)
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From 41,560 to 41050 years ago, the Earth’s magnetic north pole moved southward, and during this Lachamp event that lasted about 500 years, the Earth’s magnetic field weakened to less than 6% of its current level. After that, the Earth’s magnetic field, which had been severely reversed, reversed again for about 250 years and returned to normal.
When the Earth’s magnetic field weakens, more cosmic-rays enter the atmosphere, transforming certain atoms into radioactive carbon-14, raising the level of these isotopes. The researchers conducted simulations of atmospheric chemistry and found that more ionizing radiation came in from solar flares, triggering changes in the atmosphere that the aurora could be observed not only in the North Pole, but all over Earth.
Extreme climate where living things are difficult to adapt
Alan Cooper, who participated in the study, said, “This led to extremely high levels of ultraviolet rays, and it is estimated that extreme climatic conditions have continued to make it difficult for living things to adapt due to lightning and high temperatures.”
During the centuries that followed, Australia turned to a drier climate, and the inland lakes dried up. The researchers argued that these changes were the cause of the extinction of many of Australia’s large animal species, such as diprotodon (the giant wombat).
Also, the time when the Lachamp incident took place was when murals were first painted in caves around the world, from Europe to Indonesia. The researchers found that bad weather and very high UV levels may have forced our ancestors to enter the caves.
Also, unfortunately, Neanderthal was extinct about 4,900 years ago, immediately after the Rachamp incident. The results of this study were published in the international journal’Science’ on February 19th.
“The Kauri tree survived during the Lachamp event, and we used the change in radiocarbon-14 in the atmosphere to pinpoint when the magnetic field collapsed,” Alan Cooper said. The kauri tree, which was accidentally discovered in New Zealand, served as a’rosetta stone’.
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