Newly published research suggests that prehistoric Homo sapiens developed innovative ways to protect themselves from increased ultraviolet (UV) radiation during periods of extreme instability in Earth’s magnetic field, while their close cousins the Neanderthals did not. While this may not have been the only reason why Neanderthals went extinct, it might very well have been the most decisive cause of their decline.
These environmental shifts, known as geomagnetic excursions (or more popularly as pole shifts), happen when Earth’s magnetic poles wander from their usual positions due to changes in the planet’s liquid outer core, and they have happened at different times throughout history. One notable event, the Laschamps excursion, occurred around 40,000 to 42,000 years ago. During this time, Earth’s magnetic field dramatically weakened to about 10 percent of its current strength, allowing much more radiation to reach the planet’s surface. The magnetic North Pole shifted from the Arctic and dropped down near the equator.
The Earth’s magnetic field, which is produced by electrical currents in the molten iron core, normally protects the planet from harmful cosmic rays and solar particles. A weakened field reduces this protection, thinning the ozone layer and increasing UV exposure.
As a result of this weakened shield, auroras that are typically seen only near the poles may have been visible across much wider areas. “Auroras would have been visible in much wider areas, possibly even near the equator,” said Agnit Mukhopadhyay, a University of Michigan researcher, in an interview with New Scientist.
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While auroras can be beautiful, in this case they would have been harbingers of doom. This surge in UV radiation would have posed a serious risk to both Homo sapiens and Neanderthals, and would have required meaningful adaptations to survive—and as Mukhopadhyay and his fellow researchers explain in a new article published in Science Advances, the evidence shows that our human ancestors rose to the challenge, while Neanderthals did not.
Spectacular Aurora borealis as seen from Abisko National Park in Sweden,of the type that would have been seen frequently over the Northern Hemisphere 41,000 years ago. (pavel.shyshkouski/CC BY-SA 4.0).
Two Closely Related Species, and Two Wildly Divergent Fates
Archaeological records indicate that Homo sapiens began creating tailored clothing during this time, using tools such as needles and hide scrapers. Raven Garvey, an anthropologist at the University of Michigan, noted in Discover Magazine that this clothing likely served a dual purpose. “Tailored clothing could have also provided another unintended benefit—protection from sun damage,” she said.
In addition to clothing, Homo sapiens increasingly used ochre—a reddish pigment made of iron oxide, clay, and silica—during this period. When applied to the skin, ochre offers natural protection against the sun.
“There have been some experimental tests that show it has sunscreen-like properties. It’s a pretty effective sunscreen, and there are also ethnographic populations that have used it primarily for that purpose,” Garvey explained.
These adaptations likely gave Homo sapiens an edge over Neanderthals, who did not seem to adopt similar sun protection measures. Some researchers believe the harsh environmental conditions brought on by the Laschamps excursion contributed to Neanderthal extinction, as their inability to adapt to increased radiation would have had lethal consequences. Scientists have been searching for reasons to explain why Neanderthals and Homo sapies met such divergent fates around 40,000 years ago, and different responses to an environmental emergency could certainly explain it.
A red ochre spring near Elland in West Yorkshire in the UK. (Humphrey Bolton/Geograph Britain and Ireland/CC BY-SA 2.0).
Seeking shelter in caves was another behavior that helped humans survive. These natural structures provided some level of protection from UV exposure.
“We found that many of those regions actually match pretty closely with early human activity from 41,000 years ago, specifically an increase in the use of caves and an increase in the use of prehistoric sunscreen,” Mukhopadhyay said.
Modeling a Catastrophe
To better understand these ancient events, researchers at the University of Michigan developed complex models simulating the effects of the Laschamps excursion. They integrated a global geomagnetic field model, a space plasma environment model, and an aurora prediction model. Using magnetic signatures locked in volcanic rocks and sediments, Mukhopadhyay and his team reconstructed a detailed 3D image of Earth’s magnetic field during the Laschamps event.
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“In the study, we combined all of the regions where the magnetic field would not have been connected, allowing cosmic radiation, or any kind of energetic particles from the Sun, to seep all the way into the ground,” Mukhopadhyay said.
While the findings are not definitive, they offer a new perspective on how early humans may have responded to climate and environmental changes.
The research implies that early Homo sapiens may have developed strategic behavioral responses to environmental stress. Though Homo sapiens and Neanderthals coexisted in Europe starting around 56,000 years ago, Neanderthals disappeared during the time of the Laschamps event, which now seems unlikely to have been a coincidence. The innovative protective strategies employed by Homo sapiens may have contributed not only to their survival but also to their eventual spread across Europe and Asia.
Prehistoric human woman applying natural sunscreen to her child’s face. (Clement Phillip/Alamy).
Could It Happen Again?
It isn’t known when the next geomagnetic excursion or pole shift will happen. But it does seem to be a matter of if rather than when, and if it happened today, it could be devastating. Satellites and navigation apps would be rendered useless, and power grids would be disrupted at a cost of up to US$48 billion each day in the United States alone. Scientists say that certain parts of the planet could become all but inhabitable for centuries, as the UV radiation reaching the Earth’s surface at those spots would be too strong to survive.
If there is any good news, it is that humans found a way to adapt and ride out the storm during the Laschamps event. Perhaps the same thing would happen this time, although at this point it does seem we are completely unprepared for such a catastrophe, while at the same time being more vulnerable—and that is deeply concerning.
Top image: Neanderthal display at the National Museum of Natural Sciences in Madrid.
Source: Tiia Monto/CC BY-SA 3.0.
By Nathan Falde
