Recent research suggests that prehistoric Homo sapiens employed sunscreen and clothing to combat increased ultraviolet (UV) radiation during periods of changes in Earth's magnetic field. Earth's magnetic poles usually align with the north and south poles but occasionally wander from their traditional geographic positions in a process called geomagnetic excursions due to changes in the liquid outer core of the planet, according to New Scientist. The last change in Earth's magnetic field, known as the Laschamps excursion, occurred around 40,000 to 42,000 years ago, during which the magnetic North Pole began to shift over Europe and dropped down near the equator, New Scientist reports.
During the Laschamps excursion, Earth's magnetic field weakened to about 10 percent of its current strength, leading to an increase in radiation reaching the planet's surface. The Earth's magnetic field, created by electrical currents from its molten iron core, extends into space and acts as a protective shield against harmful radiation, including cosmic rays and charged particles from the Sun. A weakened magnetic field would have allowed more solar and cosmic radiation to reach Earth's surface, which thins Earth's ozone layer and allows more ultraviolet light to reach the surface.
"Auroras would have been visible in much wider areas, possibly even near the equator," said Agnit Mukhopadhyay, a researcher at the University of Michigan, according to New Scientist.
The weakened magnetic field allowed more UV light to penetrate the atmosphere, making Homo sapiens and Neanderthals more vulnerable to its effects. Archaeological evidence shows that during this period, Homo sapiens started sewing clothing, utilizing tools such as needles and scrapers for hide production. "Tailored clothing could have also provided another unintended benefit—protection from sun damage," said Raven Garvey, an anthropologist at the University of Michigan, according to Discover Magazine.
Furthermore, Homo sapiens were using a pigment called ochre with greater frequency around the time of the Laschamps excursion. Ochre, a reddish mineral composed of iron oxide, clay, and silica, has sun-protective properties when applied to the skin. "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, according to Discover Magazine.
These protective strategies may have given Homo sapiens an advantage over Neanderthals, who did not appear to make the same sun protection adaptations. Some researchers suggest the Laschamps event could have pushed Neanderthals towards extinction, possibly due to their lack of skills to cope with the increased radiation and environmental changes. "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," Garvey said.
Living in caves provided some protection from UV rays. "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," said Mukhopadhyay, a University of Michigan researcher.
Researchers at the University of Michigan developed models to estimate how the Laschamps excursion changed Earth's magnetic field and its effects, combining a global geomagnetic field model, a space plasma environment model, and an aurora prediction model. By studying magnetic signatures preserved in volcanic rocks and sediments, Mukhopadhyay and his colleagues created a detailed 3D reconstruction of Earth's magnetic field during the Laschamps event. "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 into the ground," Mukhopadhyay said.
"I think it's important to note that these findings are correlational and ours is a meta-analysis, if you will. But I think it is a fresh perspective on these data in light of the Laschamps excursion," she said, according to Science Focus.
The research suggests that ancient humans may have adapted to environmental changes. "These environmental changes may have driven adaptive behaviors in human populations, such as the increased use of protective clothing and ochre for UV shielding," Mukhopadhyay said.
Although Homo sapiens and Neanderthals coexisted in Europe starting about 56,000 years ago, Neanderthals became extinct during the period of the Laschamps event. The protective strategies employed by Homo sapiens may have played a role in their survival and expansion throughout Europe and Asia.
The article was written with the assistance of a news analysis system
