Sunscreen may have been essential to the survival of prehistoric humans at a time when Neanderthals were dying out, according to a recent study by researchers at the University of Michigan.
European Homo sapiens may have protected themselves from harmful solar radiation using ochre: a natural mineral, known for its rich yellow, red and brown hues, that can act as a sunscreen when applied to the skin.
This was at a time – between 41,000 and 39,000 years ago – during a period of unusual activity in Earth’s magnetic field that left early humans at particular risk of Sun damage.
The magnetic field is generated by electrical currents from the Earth's core, creating an invisible halo that protects us against cosmic radiation and charged particles from the Sun.
The North and South poles act as the north and south of the magnetic field – but that's not fixed. It is possible for the poles to wander from their geographical positions and for the strength of the magnetic field to change.
The last time this happened was around 40,000 years ago, called the Laschamps excursion. Scientists at the University of Michigan recently developed models to estimate how this excursion would have changed the Earth’s magnetic field, and calculate any knock-on effects.
"During the Laschamps event, the magnetic poles shifted away from true north," Dr Agnit Mukhopadhyay, lead author and U-M research affiliate in climate and space sciences and engineering, told BBC Science Focus.
"This movement, coupled with a notable weakening of the magnetic field, resulted in an expanded auroral zone and increased atmospheric penetration by energetic particles, such as solar energetic particles and cosmic radiation."
The scientists estimated that the Earth’s magnetic field would have reduced to approximately 10 per cent of its current strength, and that the North Pole would have drooped down near the Earth’s equator, during the Laschamps excursion.
As a result, auroras – spectacular light shows that are usually only visible near the poles – would have been visible all over Europe and into northern Africa.
Their calculations also show that Homo sapiens and Neanderthals would have been much more vulnerable to the harmful effects of ultraviolet light.
“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,” said Mukhopadhyay in a statement.
“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.”
Raven Garvey, associate professor of anthropology at the University of Michigan and co-author of the study, told BBC Science Focus that we don't know exactly how early humans reacted to increased exposure to harmful radiation. But archaeological sites dating to the same period show increased use of ochre.
"Ochre has multiple known uses, including as a sunscreen," she said. "So, while archaeologists cannot directly observe the behaviours of peoples who lived over 40,000 years ago, we can hypothesise that the increased use of ochre may have been, in part, for its sun-protective properties."
From around the same time, archaeologists have found evidence of tools associated with sewing, including needles, which suggests early humans were making well-fitting clothes – keeping them warm and protected from the sun.
Meanwhile, Neanderthals were dying out in Europe – perhaps partially because they did not have these skills.
This study, published in Science Advances, was only correlational, so it doesn’t prove that humans outlived Neanderthals because they were better able to cope with the Laschamps excursion.
However, Garvey said in a statement that it offered a “fresh perspective” on what might have happened 40,000 years ago.
Read more:
- A scientist’s guide to life: how to stay safe in the Sun
- Earth's magnetic field is overdue a flip. Should we be worried?
- How strong does a magnetic field have to be to affect the human body?
About our experts:
Dr Agnit Mukhopadhyay is a space physicist who specialises in mapping, geosciences and mathematical modelling. He is a research affiliate in climate and space sciences and engineering at the University of Michigan and a senior software engineer at MathWorks. Mukhopadhyay designs and implements functionalities that are commercially used in mapping the Earth and other planetary bodies.
Dr Raven Garvey is an associate professor of anthropology at the University of Michigan and an associate curator at the Museum of Anthropological Archaeology. She studies the influences of ecological, demographic, and social factors on Holocene hunter-gatherers’ behaviours and broader cultural change through time. Garvey's current field projects combine archaeological data with evolutionary modelling to address questions at the intersection of human behavioural ecology and cultural transmission theory.
