Lack of "prehistoric sunscreen" may have killed the Neanderthals

Around 41,000 years ago, Earth’s magnetic field underwent a chaotic shift that temporarily weakened the planet’s natural protection from harmful solar radiation.

A new study suggests that early Homo sapiens may have survived – and even thrived – through this period thanks to innovations including tailored clothing, increased use of sun-protective ochre, and strategic sheltering in caves.

Meanwhile, their relatives the Neanderthals, who lacked these adaptations, vanished shortly thereafter.

The experts used advanced 3D modeling and archaeological evidence to offer a fresh perspective on how one of Earth’s past geomagnetic upheavals – known as the Laschamps excursion – may have influenced human evolution and migration.

The sky lit up over Europe

The Laschamps excursion was a geomagnetic event that occurred about 41,000 years ago, during which Earth’s magnetic field temporarily weakened to about 10% of its current strength.

While the magnetic poles didn’t fully flip, they did wander significantly – especially over Europe – bringing intense auroras and letting in greater amounts of harmful ultraviolet (UV) radiation.

“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 in to the ground,” said lead author Agnit Mukhopadhyay, a research affiliate in climate and space sciences and engineering at University of Michigan.

“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.”

Magnetism and wandering poles

Earth’s magnetic field is generated by the rotation of its molten iron core, creating electrical currents that produce a magnetic shield around the planet.

This field deflects most of the solar wind and cosmic rays that would otherwise reach Earth’s surface and deplete its ozone layer.

When the field weakens, as it did during the Laschamps event, it exposes much more of the planet to radiation.

To explore this ancient episode, the researchers used the Space Weather Modeling Framework – a tool developed at UM’s Center for Space Environment Modeling – to simulate how the Earth’s magnetic field and space plasma system interacted during the Laschamps event.

The experts then reconstructed the global space environment in 3D by combining models of the geomagnetic field, the surrounding plasma, and auroral activity at the time.

The resulting simulations revealed a planet dramatically different from what we know today: auroras visible across Europe and northern Africa, and large swaths of the Earth exposed to solar and cosmic radiation.

Why did Neanderthals vanish?

This intense solar exposure, researchers suggest, could have pushed early humans to adopt protective strategies. By around 41,000 years ago, Homo sapiens were becoming increasingly common in Europe, while Neanderthals were nearing extinction and soon vanished.

“What some of the differences are between these species, between Neanderthals and anatomically modern humans, that might account for that disappearance has been a major anthropological question for decades,” said Raven Garvey, a U-M associate professor of anthropology.

One possibility? Tailored clothing. Archaeological sites associated with Homo sapiens from this period show evidence of sewing tools – scrapers, awls, and needles – that allowed for the creation of fitted garments.

Such clothing would have helped protect against cold climates but also may have shielded skin from increased UV exposure.

According to the scientists, tailored clothing has a two-fold benefit: it is significantly warmer and this added warmth meant that early humans could travel farther from their hearths and shelters in their search of food.

Human adaptation and innovation

Clothing wasn’t the only adaptation. Homo sapiens also began using ochre more frequently during this period.

Ochre, a naturally occurring red or yellow pigment composed of iron oxide, has long been used by human ancestors for decorative and symbolic purposes. But it also has practical benefits.

“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 said.

“Its increased production and its association primarily with anatomically modern humans (during the Laschamps) is also suggestive of people’s having used it for this purpose as well.”

Response to an invisible threat

Another clue lies in early humans’ use of caves. Archaeological data show a marked increase in cave habitation around the same time as the Laschamps event.

These natural shelters would have provided physical protection from the radiation pouring in through the weakened magnetic field.

As Mukhopadhyay and Garvey note, these behaviors – hiding in caves, making more use of ochre, and sewing fitted clothes – are all found in archaeological records.

The records date back to the Laschamps event, hinting at a collective response to an invisible but potentially deadly threat.

Magnetic field stability and human survival

Garvey is careful to emphasize that the study’s findings. “I think it’s important to note that these findings are correlational and (ours is a) meta analysis, if you will,” she said. “But I think it is a fresh perspective on these data in light of the Laschamps excursion.”

While not proof of causation, the overlap between increased human technological behavior and periods of magnetic field instability offers new insight into how Homo sapiens may have gained a survival advantage over Neanderthals.

Future magnetic field reversal

Beyond its relevance to human prehistory, the study also raises questions about how a future magnetic reversal might affect modern life.

With Earth’s magnetic field currently weakening and the North Pole slowly drifting, Mukhopadhyay says it’s worth considering what would happen if a similar event occurred today.

“If such an event were to happen today, we would see a complete blackout in several different sectors,” he warned.

“Our communication satellites would not work. Many of our telecommunication arrays, which are on the ground, would be severely affected by the smallest of space weather events, not to mention the human impacts which would also play a pretty massive role in our day-to-day lives.”

Could humans vanish like Neanderthals?

The research also carries implications for astrobiology. “Many people say that a planet cannot sustain life without a strong magnetic field,” Mukhopadhyay said.

“Looking at prehistoric Earth, and especially at events like this, helps us study exoplanetary physics from a very different vantage point. Life did exist back then. But it was a little bit different than it is today.”

In the end, the Laschamps excursion offers more than just an explanation for why Neanderthals may have vanished. It’s a reminder that Earth’s magnetic shield, often taken for granted, plays a crucial role in protecting life on our planet. And when it falters, survival may depend on how quickly life can adapt.

The study is published in the journal Science Advances.

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