Modeling of Earth's atmosphere and magnetic field 41,000 years ago suggests how the
Homo sapiens strategy for dealing with the sun helped them survive as a species. Just because Homo sapiens hadn't yet developed SPF sun protection doesn't mean they didn't know that solar radiation could be dangerous.
Homo sapiens used sunscreen in one form or another, protected themselves from UV rays with clothing and avoided sunstroke by hiding in caves, according to a paper published in the journal Science Advances.
In fact, these strategies may have helped their populations spread across Europe and Asia at a time when Neanderthals, who apparently made no such adaptations, were declining in numbers.
"What differences between these species, between Neanderthals and anatomically modern humans, that might explain this extinction have been a major anthropological question for decades," Raven Garvey, an anthropologist at the University of Michigan and an author of the study, said in a press release.
Strategies for coping with the sun in Homo sapiens
The researchers found that these sun-fighting strategies roughly coincided with the period when the North Pole approached Europe, as the poles of Earth's magnetic field began to move - a process that has occurred about 180 times over the lifetime of
Earth. This process weakened the magnetic field, caused the southern and northern lights to appear over much of the globe, and allowed more ultraviolet light to pass through the atmosphere.
Meanwhile, archaeological evidence suggests that during this period Homo sapiens began sewing clothes and rubbing ochre, a mineral that blocks sunlight, on their skin. Living in caves then also provided some protection.
"In the study, we combined all the regions where the magnetic field would not have acted, allowing cosmic radiation or any energetic particles from the sun to seep down to the ground," Agnit Mukhopadhyaya, an author of the paper and researcher at the University of Michigan, said in a press release. "We found that many of these regions coincide quite closely with early human activity 41,000 years ago, particularly the increased use of caves and the use of prehistoric sunscreens."
Earth's magnetic field
To reach this conclusion, Mukhopadhyaya used existing models and built his own. First, he built a simulation of how the Earth's magnetic field, created by its rotation, spreads a protective halo around the globe. This halo protects the Earth from cosmic radiation, which thins the planet's ozone layer, thereby letting more ultraviolet light in.
Next, he studied how the hot gases and charged particles that
the Sun ejects onto Earth act as a plasma system. Mukhopadhyaya then developed a model predicting how this system interacts with the Earth's magnetic field.
This magnetic field leads to the formation of auroras, so people usually see them only near the north and south poles, because that is where the magnetic attraction is strongest. However, sometimes the poles change places - the last such event happened just about 41,000 years ago.
The effects of the atmosphere on Homo sapiens
Mukhopadhyaya, working with Sanjda Panowska, a researcher at Germany's Helmholtz Center for Geosciences "GFZ," essentially combined three models from that time period into one: the Earth's geomagnetic field, the surrounding cosmic plasma field, and auroral activity. This combination produced a three-dimensional picture illustrating where charged particles could most easily slip through the planet's geomagnetic field.
The model showed that during the pole shift 41,000 years ago, the Earth's magnetic field shrank to about 10 percent of its current strength. The poles dropped toward the equator, the magnetic field expanded, and the auroras would have been visible throughout Europe and North Africa.
Photo: auroreboreale.net
The researchers then overlaid this combined 3D map of Earth's atmospheric and electromagnetic systems on a globe and marked where Homo sapiens and
Neanderthals lived. These two groups of early and modern humans coexisted in Europe about 56,000 years ago. About 16,000 years later, Neanderthals ceased to dominate Europe.
Sunscreen and clothing of prehistoric humans
It is possible that tailored clothing also helped. Archaeologists have found needles and awls, tools associated with sewing, at Homo sapiens sites, but not at Neanderthal sites. Sewn clothing not only kept people warm when they emerged from caves, allowing them to hunt longer and at greater distances from home. It also protected them from ultraviolet rays.
Whether this was intentional or not is debatable, because "clothing may have provided another unintended benefit - protection from sunlight," Garvey says. "Solar radiation protection also provided significant benefits to anyone who possessed it."
There is evidence that Homo sapiens used ochre, a pigment composed of iron oxide, a clay, not only to color objects but also to protect their bodies from ultraviolet radiation.
"There have been some experimental studies that have shown that it has sunscreen-like properties. It's a pretty effective sunscreen, and there are ethnographic populations that have used it primarily for that purpose," Garvey says.