Weird space weather seems to have influenced human behavior on Earth 41,000 years ago – our unusual scientific collaboration explores how

Our first meeting was a bit awkward. One of us is an archaeologist who studies how past peoples interacted with their environments. Two of us are geophysicists who investigate interactions between solar activity and Earth’s magnetic field.

When we first got together, we wondered whether our unconventional project, linking space weather and human behavior, could actually bridge such a vast disciplinary divide. Now, two years on, we believe the payoffs – personal, professional and scientific – were well worth the initial discomfort.

Our collaboration, which culminated in a recent paper in the journal Science Advances, began with a single question: What happened to life on Earth when the planet’s magnetic field nearly collapsed roughly 41,000 years ago?

Weirdness when Earth’s magnetic shield falters

This near-collapse is known as the Laschamps Excursion, a brief but extreme geomagnetic event named for the volcanic fields in France where it was first identified. At the time of the Laschamps Excursion, near the end of the Pleistocene epoch, Earth’s magnetic poles didn’t reverse as they do every few hundred thousand years. Instead, they wandered, erratically and rapidly, over thousands of miles. At the same time, the strength of the magnetic field dropped to less than 10% of its modern day intensity.

So, instead of behaving like a stable bar magnet – a dipole – as it usually does, the Earth’s magnetic field fractured into multiple weak poles across the planet. As a result, the protective force field scientists call the magnetosphere became distorted and leaky.

The magnetosphere normally deflects much of the solar wind and harmful ultraviolet radiation that would otherwise reach Earth’s surface.

So, during the Laschamps Excursion when the magnetosphere broke down, our models suggest a number of near-Earth effects. While there is still work to be done to precisely characterize these effects, we do know they included auroras – normally seen only in skies near the poles as the Northern Lights or Southern Lights – wandering toward the equator, and significantly higher-than-present-day doses of harmful solar radiation.

The skies 41,000 years ago may have been both spectacular and threatening. When we realized this, we two geophysicists wanted to know whether this could have affected people living at the time.

The archaeologist’s answer was absolutely.

Human responses to ancient space weather

For people on the ground at that time, auroras may have been the most immediate and striking effect, perhaps inspiring awe, fear, ritual behavior or something else entirely. But the archaeological record is notoriously limited in its ability to capture these kinds of cognitive or emotional responses.

Researchers are on firmer ground when it comes to the physiological impacts of increased UV radiation. With the weakened magnetic field, more harmful radiation would have reached Earth’s surface, elevating risk of sunburn, eye damage, birth defects, and other health issues.

In response, people may have adopted practical measures: spending more time in caves, producing tailored clothing for better coverage, or applying mineral pigment “sunscreen” made of ochre to their skin. As we describe in our recent paper, the frequency of these behaviors indeed appears to have increased across parts of Europe, where effects of the Laschamps Excursion were pronounced and prolonged.

At this time, both Neanderthals and members of our species, Homo sapiens, were living in Europe, though their geographic distributions likely overlapped only in certain regions. The archaeological record suggests that different populations exhibited distinct approaches to environmental challenges, with some groups perhaps more reliant on shelter or material culture for protection.

Importantly, we’re not suggesting that space weather alone caused an increase in these behaviors or, certainly, that the Laschamps caused Neanderthals to go extinct, which is one misinterpretation of our research. But it could have been a contributing factor – an invisible but powerful force that influenced innovation and adaptability.

Cross-discipline collaboration

Collaborating across such a disciplinary gap was, at first, daunting. But it turned out to be deeply rewarding.

Archaeologists are used to reconstructing now-invisible phenomena like climate. We can’t measure past temperatures or precipitation directly, but they’ve left traces for us to interpret if we know where and how to look.

But even archaeologists who’ve spent years studying the effects of climate on past behaviors and technologies may not have considered the effects of the geomagnetic field and space weather. These effects, too, are invisible, powerful and best understood through indirect evidence and modeling. Archaeologists can treat space weather as a vital component of Earth’s environmental history and future forecasting.

Likewise, geophysicists, who typically work with large datasets, models and simulations, may not always engage with some of the stakes of space weather. Archaeology adds a human dimension to the science. It reminds us that the effects of space weather don’t stop at the ionosphere. They can ripple down into the lived experiences of people on the ground, influencing how they adapt, create and survive.

The Laschamps Excursion wasn’t a fluke or a one-off. Similar disruptions of Earth’s magnetic field have happened before and will happen again. Understanding how ancient humans responded can provide insight into how future events might affect our world – and perhaps even help us prepare.

Our unconventional collaboration has shown us how much we can learn, how our perspective changes, when we cross disciplinary boundaries. Space may be vast, but it connects us all. And sometimes, building a bridge between Earth and space starts with the smallest things, such as ochre, or a coat, or even sunscreen.

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