Sunscreen may have kept ancient humans alive during a polar reversal
Despite the sunscreen misinformation you might see online, ancient humans did face problems from the sun's harmful rays. Ancient Homo sapiens about 40,000 years ago may have even benefited from some of the same technologies that we use to avoid sunburns today–mineral sunscreen, tailored clothes, and using caves for shade and shelter. These advances may have been particularly advantageous when Earth's magnetic poles switched a bit, according to a study published April 16 in the journal Science Advances.
Earth's magnetic field is created by its rotation, as well as the rotation of our planet's core. The core, which is made up of molten iron, generates electrical currents. These currents extend a sort of halo around the globe that helps protect Earth from cosmic radiation. This radiation thins Earth's ozone layer and lets in more ultra violet (UV) and the interaction of these particles with the Earth's magnetic field also results in aurora.
Currently, this magnetic field has a north and south orientation in the form of Earth's North and South poles. This is why you typically see auroras in regions close to the poles, where magnetic fields are the strongest.
Occasionally, these poles wander from their traditional geographic positions. These are called geomagnetic excursions. This natural process has occurred roughly 180 times over our planet's 4.5 billion-year geological history. Scientists believe that it is caused by some instability in the processes that generate Earth's magnetic field.
The most recent geomagnetic excursion is called the Laschamps excursion and occurred about 41 to 42,000 years ago, when the magnetic North Pole began to shift over Europe. During this reversal, the magnetic field weakened, causing aurora over most of the globe and allowed more harmful UV light to come in from space.
[ Related: A geomagnetic curveball 42,000 years ago changed our planet forever. ]
Around this same time, archeological evidence shows that Homo sapiens were likely making tailored clothing for themselves and using a pigment called ochre with greater frequency. Ochre itself has some sun-protective properties when applied to the skin and may have helped ancient humans spread throughout present-day Europe and Asia as the Neanderthal population was declining.
'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,' study co-author Agnit Mukhopadhyay, a space physicist at the University of Michigan, said 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.'
The team built models of the interaction of space particles and Earth's magnetic field using the Space Weather Modeling Framework. Mukhopadhyay developed a model that predicts how this plasma system will interact with Earth's magnetic field–ultmately forming an aurora.
Working with Sanja Panovska from Germany's GFZ Helmholtz Centre for Geosciences, Mukhopadhyay created a 3D reconstruction of Earth's geospace system. They combined three separate models: a global model that reconstructs the geomagnetic field during the Laschamps excursion, one model of the space plasma environment around Earth, and another model that predicted what Earth's aurora looked like at the time. The resulting 3D model showed where charged particles were able to slip through Earth's geomagnetic field.
During the Laschamps excursion, Earth's magnetic field reduced in size to about 10 percent of its current strength. As a result, Earth's magnetic poles drooped down near the equator and the magnetic field lines expanded. This expansion meant the aurora could have been visible all over Europe and into northern Africa.
When the team laid their 3D map of Earth's space system over the world, they found that the time period of the Laschamps excursion coincided with periods of change for groups of humans living on the planet
Homo sapiens and Neanderthals coexisted in Europe beginning roughly 56,000 years ago. However, Neanderthals were no longer identified as a species in Europe by about 40,000 years ago.
'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,' study co-author and University of Michigan anthropologist Raven Garvey, said in a statement.
Garvey suggests that clothing itself might have been a major difference between the species. The technological means of making clothing that fitted to the body have been discovered at archaeological sites associated with anatomically modern humans, but not necessarily sites where Neanderthals lived.
Archaeologists have found scrapers used in hide production, as well as needles and awls needed for sewing at sites associated with anatomically modern humans. According to Garvey, tailored clothing like this was significantly warmer. This added warmth meant that people could travel farther to find food and provided protection from sun damage, she said.
[ Related: Ice age humans made needles from animal bones, archeologists discover. ]
Because there are multiple detrimental effects of solar radiation, including potentially increased infant mortality, 'having protection against solar radiation would also have conferred significant advantage to anyone who possessed it,' Garvey said.
Additionally, ancient humans may have ramped up their use of ochre. This naturally occurring pigment is composed of iron oxide, clay, and silica and has been used by several species of hominins for thousands of years. People used it to paint objects, on cave walls and even to decorate their bodies.
'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. '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.'
According to the team, while these findings are not definitive, they offer a new way to look at already existing data.
'I think it's important to note that these findings are correlational and (ours is a) meta analysis, if you will,' Garvey said. 'But I think it is a fresh perspective on these data in light of the Laschamps excursion.'
The 3D model offers us a way to predict how future excursions might affect us. If a reversal like this were to occur today, we could see complete blackouts with communication satellites not working, telecommunications in disarray. These types of events have already happened, even during smaller space weather events.
This work also highlights that humans were still able to survive on a planet whose atmosphere looked a lot different than ours does today.
'Many people say that a planet cannot sustain life without a strong magnetic field,' Mukhopadhyay said. 'Looking at prehistoric Earth, and especially at events like this, helps us study exoplanetary physics from a very different vantage point. Life did exist back then. But it was a little bit different than it is today.'
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