Roughly 41,000 years ago, our planet underwent a magnetic identity crisis and it may have quietly helped Homo sapiens outlast their Neanderthal cousins. According to new research from the University of Michigan, a dramatic weakening of Earth’s magnetic field, known as the Laschamps excursion, triggered a spike in cosmic radiation. While the skies lit up with auroras, the surface below was bombarded with harmful UV rays. But humans, resourceful as ever, may have found clever ways to survive from living in caves to inventing prehistoric sunscreen.
The Earth’s magnetic field is our planet’s invisible guardian, generated by electrical currents swirling in its molten outer core. It normally directs radiation away from the surface and is most concentrated at the poles — hence the auroras dancing in polar skies. But this protective shell isn’t fixed. In fact, it’s prone to wandering and even reversing completely. These episodes, called geomagnetic excursions, have happened over 180 times in Earth’s history.
One of the most dramatic, the Laschamps excursion, occurred between 42,200 and 41,500 years ago. During this time, the magnetic field shrank to just 10% of its usual strength. In this weakened state, the Earth was flooded with ultraviolet and cosmic radiation, leading to a temporarily depleted ozone layer. The usual planetary defenses were down and life on the surface faced the consequences.
A team of researchers led by University of Michigan scientists used 3D simulations to model what the Earth’s magnetic field looked like during this magnetic anomaly. They discovered that this era overlapped with the final days of Neanderthals and a critical phase of human evolution. The radiation exposure posed serious biological risks, such as increased chances of birth defects and eye damage.
But not all hominins were equally vulnerable. Homo sapiens seemed to adapt.
Archaeological findings reveal a surge in the use of cave shelters, offering natural protection from the relentless UV rays. Additionally, bone tools like awls and needles suggest a leap in clothing technology. These garments likely provided not only insulation but also protection from radiation, allowing humans to roam further in daylight.
Then there’s the curious case of ochre a reddish or yellow mineral pigment found more frequently at sites dating to this turbulent period. While typically associated with ancient art, ochre had a more practical use. When applied to the skin, its iron-rich composition worked much like a primitive sunscreen.
“It’s a pretty effective sunscreen,” explains Raven Garvey, associate professor of anthropology at U-M. “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.”
Though the findings are correlational, they offer a compelling hypothesis: perhaps it wasn’t just intelligence or luck that helped Homo sapiens flourish while Neanderthals vanished maybe it was also a flair for adaptation under solar duress.
The research was published in Science Advances.
Source: University of Michigan
