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The South Pole Telescope is located near the geographic pole in Antarctica.
The poles were briefly reversed 41,000 years ago
Photo: HANDOUT / REUTERS
The earth's magnetic field can be capricious.
It surrounds the globe and is created by currents of liquid iron in the outer core of the earth.
This is of enormous benefit to humanity.
Because people have orientated themselves for centuries using the compass.
In addition, the magnetic field protects the earth from cosmic rays.
But its strength fluctuates constantly.
The magnetic poles migrate, sometimes reverse completely, and may continue to do so in the future.
A brief reversal last occurred a little more than 41,000 years ago, known in science as the "Laschamps event".
The magnetic north and south poles were reversed for less than 500 years, during which time the earth's magnetic field only reached around 28 percent of its current strength.
Researchers have now examined this event more closely.
They believe that the reversal of the Earth's magnetic field changed the Earth's atmosphere and climate significantly.
The consequences for life on earth were possibly serious, write Alan Cooper from the South Australian Museum in Adelaide and Chris Turney from the University of New South Wales in Sydney in the journal Science.
As the researchers based in Australia report, lakes could have dried out and large parts of North America iced over.
Perhaps even the extinction of numerous animals and the disappearance of the Neanderthals were promoted.
Cooper and Turney report that the magnetic field was temporarily even weaker in the time before the first polarity reversal and was only around six percent of the current value.
The researchers named this phenomenon about 42,000 years ago the “Adams event”, named after the science fiction author Douglas Adams.
In their investigation, the scientists used giant kauri trees (Agathis australis), which grew in New Zealand more than 40,000 years ago and had been preserved in swamps.
Your tree rings cover a period of 1700 years - and thus also the time of magnetic turbulence.
The growth rings contain indications of the amount of the radioactive carbon isotope C-14, which is used for determining the age with the radiocarbon method.
C-14 is formed in the atmosphere when cosmic rays hit nitrogen.
An increased proportion of C-14 in wood indicates an increased penetration of cosmic radiation and thus a weaker earth's magnetic field.
With the tree rings, the number of C-14 in the atmosphere could be resolved very precisely over time for the first time.
"The subfossil kauri trees are an exciting archive of the atmospheric composition," says the paleoclimatologist Florian Adolphi from the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI), who was involved in the study, in a press release.
The researchers linked the data obtained with other data sets, such as analyzes of ice and sediment drill cores, for precise chronological classification.
"The ionized air sizzled the ozone layer."
Study author Chris Turney, University of New South Wales
Using computer models, the researchers simulated how the increased cosmic radiation affected the chemistry of the atmosphere, which also affects the climate.
Among other things, they found that the weakening of the earth's magnetic field had led to a decrease in ozone.
"Unfiltered radiation from space tore apart air particles in the earth's atmosphere, separated electrons and emitted light - a process called ionization," explains Turney.
"The ionized air sizzled the ozone layer."
According to the researchers, this triggered a wave of changes in the atmosphere.
This also included more dazzling plays of light, which we know as northern lights, and which at that time could have been observed not only near the poles, but across the globe.
Extinction of the Neanderthal man due to magnetic field questionable
The precise analysis of the "Laschamps event" enabled the researchers to relate the weakening of the Earth's magnetic field to numerous anomalies in sediments and volcanic rocks from 41,000 to 42,000 years ago.
They hypothesize the effects in their article numerous times.
As a climatic consequence of the magnetic field weakening, large lakes in Australia could have dried up, the researchers write.
Elevated surface temperatures in Europe and lower in North America, as well as the growth of the ice sheet in North America shortly after the event, could also be related.
In addition, the weaker magnetic field and the associated increased levels of ultraviolet radiation could have led to the extinction of large mammals in Australia and even the Neanderthals in Europe, the scientists explain, referring to earlier studies.
The increased occurrence of cave paintings in Europe and Southeast Asia could be related to the fact that people at that time increasingly sought protection from the sun in caves.
In an accompanying article, "Science" editor Paul Voosen writes that in addition to agreeing with the researchers' theses, there is also contradiction.
Anders Svensson, a glaciologist at the University of Copenhagen, says that no corresponding signals can be found in ice cores from Greenland and Antarctica.
Thomas Higham, archaeologist and radiocarbon expert at the University of Oxford, believes the link between the weakness of the earth's magnetic field and human development is speculative, according to the article.
None of the milestones in human evolution corresponded well with the polarity reversals 42,000 years ago and none occurred suddenly.
The researcher Norbert Nowaczyk from the German Research Center for Geosciences in Potsdam, who was also involved in the study, does not consider such causal relationships to be excluded, but rather improbable.
Today's climate is also influenced by the earth's magnetic field, which has been weakening again for around 2000 years.
Since the first direct measurement 170 years ago, it has become around nine percent weaker.
Whether this heralds a pole reversal is controversial.
What is certain is that magnetic turbulence is likely to have a serious impact on our society, which is largely based on electronics.
At least in the animal world, this could already be the case.
Because solar storms disrupt the Earth's magnetic field, whales could easily become disoriented and stranded on coasts more often.
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joe / dpa
