The earth's magnetic field weakens

When the earth's magnetic field tilted

The magnetic north pole does not have a permanent position. He likes to wander. Very rarely does it happen that the earth's magnetic field is reversed and the North Pole becomes the South Pole. The last such pole shift took place around 42,000 years ago. At that time, the magnetic field weakened at times to up to six percent of its current strength. Overall, the polarity reversal did not last long, after around 800 years the "excursion" was over again. The last sustained polarity reversal was around 780,000 years ago.

An international study led by the University of New South Wales (UNSW) in Sydney and the South Australian Museum is now trying to paint a picture of what happened on earth 42,000 years ago. The analysis in the journal “Science” resembles a horror scenario: The researchers speak of “apocalyptic conditions” that would have ruled the earth for several centuries due to the reversal of the earth's magnetic field and the resulting increased radiation effects of the sun. This had "far-reaching consequences for our planet," commented the researchers in the academic magazine "The Conversation".

After the strength of the magnetic field fell to less than six percent of today's value during the pole shift, the earth temporarily lost its protective shield against cosmic radiation. The ozone layer was subsequently destroyed and electrical storms raged over the tropics - according to the researchers. Without the protection of the magnetic field and the ozone layer, life on earth was exposed to intense ultraviolet light. "It must have felt like the end of the world," said Alan Cooper of the South Australian Museum, who was involved in the study.

The researchers owe their findings to a »contemporary witness«. About two years ago construction workers in New Zealand discovered an ancient kauri tree - perfectly preserved in the bog. This massive tree was growing at the time of the last pole shift, and its annual rings were so well preserved that the researchers were able to use climate models and radiocarbon dating to build a time scale that represented this dramatic period in Earth's history. "This enabled us to accurately date the time and environmental impact of the last pole shift for the first time," said Chris Turney of UNSW, one of the study's lead authors. The team compared this time scale with records from caves, ice cores and peat bogs from around the world.

The researchers found that the growth of ice sheets and glaciers over North America as well as large shifts in the weather systems can possibly be traced back to the pole shift. One of their first indications was that the megafauna on mainland Australia and Tasmania - giant kangaroos and giant wombats - also became extinct around 42,000 years ago. "That never seemed right, because it was long after the Aboriginal people arrived, but around the same time the Australian environment was changing to its current dry state," Cooper said.

But the researchers go even further. They believe that the polarity reversal at that time could also be responsible for the extinction of the Neanderthals. At the same time, they consider it no coincidence that figurative cave painting also developed at this point in time. Modern humans probably sought refuge in caves during this period, they conclude.

The researchers' far-reaching conclusions have sparked heated debates in the scientific community. For some colleagues, the assumptions go too far, as the numerous comments in "The Conversation" make clear. But the secrets that the ancient kauri tree has revealed definitely show the far-reaching consequences a pole shift has on life on earth.

And they represent a warning: Because even today, a renewed pole shift is not completely absurd. For example, some scientists have recently expressed concern about the current movement of the North Magnetic Pole. This could - coupled with the weakening of the Earth's magnetic field by around nine percent in the last 170 years - "point to an imminent reversal," said Cooper. Even today, the consequences for modern society would be enormous: Cosmic radiation would not only disrupt our electricity and satellite networks, according to Turney a pole reversal would also be an "unprecedented accelerator" of the man-made climate crisis.

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