Ochre body paint may have been a form of prehistoric sunscreen that helped early humans survive a sudden increase in ultraviolet (UV) radiation around 41,000 years ago.
That’s a fascinating new hypothesis recently put forward by an international team of geoscientists and anthropologists, led by researchers at the University of Michigan.
Their study reconstructs the global space environment during the end of the Last Glacial Period, and it finds that when Earth’s magnetic field suddenly hiccuped all those millennia ago, it had a profound impact on our planet’s protective solar shield.
Scientists already knew of this distinct geomagnetic tantrum in Earth’s history, called the Laschamp event, when the poles suddenly and briefly went haywire and underwent a partial flip before settling back into their original positions.
But the new model is more detailed than ever before, and it shows that over the course of thousands of years, while the event was underway, the strength of Earth’s geomagnetic field plummeted, reaching just 10 percent of what it is today.
At the same time, the poles where magnetic field lines meet expanded and tilted by over 75 degrees relative to Earth’s rotational axis.
The South Pole shifted away from Antarctica and settled over Australia and New Zealand, while the North Pole wandered out of the Arctic into Western Eurasia, Northern Africa, and the northwestern Sahara.
“Vast expanses of both hemispheres were enveloped by expansive open field line regions, unleashing a substantial barrage of auroral precipitation on a global scale,” the authors write.
That’s where the sunscreen comes in handy.
Auroras are caused by charged particles from the Sun, which are guided along Earth’s magnetic field lines to the poles, where they are dumped out and interact with our planet’s atmosphere.
If the magnetic field lines are weakened, though, all that cosmic radiation enters the atmosphere earlier and deeper, which can be disastrous for the ozone layer below. As this protective layer weakens, it in turn admits more harmful UV light.
During the Laschamp weakening, if some parts of the world let in more UV radiation, then early humans, including our own species and Neanderthals, were likely affected.
Scientists have previously suggested our species’ adaptations to the Laschamp event may have allowed us to survive where other humans could not.
The new study, led by space physicist Agnit Mukhopadhyay, adds to that idea.
“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,” explains Mukhopadhyay.
While speculative, the authors point out that many of the areas likely exposed to increased ultraviolet radiation matched closely with changes in human activity more than 40,000 years ago, including more tools for tailoring clothing, an increase in cave art, and the use of ochre, which some studies suggest is a natural prehistoric sunscreen.
These behaviors may reflect humanity’s attempt to minimize exposure to ultraviolet radiation. To this day, the Himba community in northern Namibia, for instance, use ochre as sunscreen, and Indigenous Australians have similar customs.
“There have been some experimental tests that show [ochre] has sunscreen-like properties. It’s a pretty effective sunscreen, and there are also ethnographic populations that have used it primarily for that purpose,” confirms anthropologist Raven Garvey of the University of Michigan.
“Its increased production and its association primarily with anatomically modern humans (during the Laschamp) is also suggestive of people’s having used it for this purpose as well.”
The timing is certainly intriguing, but the fossil record is not a complete one, and it needs to be interpreted with caution. There are likely many factors that led to our species’ survival – and to the demise of our cousins.
The disappearance of the Neanderthals, for instance, largely coincides with the Laschamp event, which has led some to propose that it is what killed our early relatives.
Today, however, there is now some archaeological evidence of Neanderthals making tools for clothing, using ochre, and making cave art. Perhaps they didn’t do this to the same level of sophistication as our own species, but they may have been adapting to the times, too. Historically, scientists have tended to underestimate our ancient cousins and what they were capable of.
In 2021, archaeologist Anna Goldfield wrote a piece for Sapiens that argued that “headlines trumpeting that a magnetic pole switch killed off our ancient relatives are vastly oversimplifying the tremendously complex system in which Neanderthals and our Homo sapiens ancestors lived.”
The new study was published in Science Advances.
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