Changes to Earth's Magnetic Field May Have Been Involved in Neanderthal Extinction

A weakening of Earth's magnetic field may have been involved in the extinction of the Neanderthals, scientists have suggested. A weak magnetic field, they say, could have led to reduced protection from ultraviolet radiation. Eventually, this could have led to health problems that contributed to the decline of our ancient relatives.

In a study published in the journal Reviews of Geophysics, James Channell, from the University of Florida, and Luigi Vigliotti, from Italy's Institute of Marine Sciences, have linked changes in Earth's geomagnetic field to the evolution and extinction of mammals, claiming that periods where the field weakens appear to correlate to extinction episodes across the world.

Earth's magnetic field extends from the planet's interior far into space. It protects the planet from the solar wind—a stream of charged particles coming from the Sun. If these particles were able to impact our atmosphere it could strip away the ozone layer that protects the planet from UV radiation.

The magnetic field is in a constant state of change. It moves around, gets stronger and weaker and occasionally reverses its poles. When this happens, the magnetic field gets weaker. During one reversal that took place around 41,000 years ago—known as the Laschamp event—the magnetic field is estimated to have fallen to just five percent of its current strength.

It is this reversal event that Channell and Vigliotti believe helped wipe out a number of mammal species in Australia and Eurasia—including Neanderthals. As the field got weaker, more UV radiation from the Sun was able to get through, impacting the health of animals and plants by damaging their DNA. Over time, this could have led to mutations that would have been detrimental to health.

Previously, the extinction of the Neanderthals had been attributed to a number of factors, including increased competition with modern humans and climate change. "Neanderthals were competing with modern humans in Europe for several thousand years, and had different skills and tool industries," Channell told Newsweek. "There is no evidence of anything dramatic such as war or genocide. Neanderthal and modern humans probably lived in distinct communities, although with occasional interbreeding."

Extinction correlations

For 25 years, Channell has been working to reconstruct Earth's magnetic field over the last two million years. "We started from knowledge of magnetic field behavior—and the correlations with mammal extinctions seemed to fall into place," he explained.

In the study, the researchers say two extinction events—one 40,000 years ago and another 13,000 years ago—both appear to have coincided with periods where Earth's magnetic field had weakened. By looking at the past 200,000 years, they say the timings of branching episodes of the human family tree can also be linked to the magnetic field, suggesting UV radiation has played a big role in our evolutionary history.

But how did us humans survive the weakening field when Neanderthals did not? Channell and Vigliotti say this is due to differences in the aryl hydrocarbon receptor (AhR). This receptor controls sensitivity to UV radiation—the study suggests that humans were better protected from the harmful effects than Neanderthals.

"The envisaged role of UVB [the radiation that causes sunburn] in reducing megafaunal populations [including Neanderthals] at the Late Quaternary extinctions does not involve an instantaneous 'blitzkrieg,' but rather an accumulation of UVB-triggered mutations over multiple [around 30] generations," Channell said.

The research has limitations. Dates relating to the weakening of the magnetic field and extinctions are not exact, so correlating the two with a high level of confidence is difficult. Furthermore, the role of AhR in relation to the effects of UV radiation in mammals is still being investigated.

Brian Thomas, Professor of Physics and Astronomy at Washburn University, Kansas, who was not involved in the study, said believes the authors "overstate the likely outcomes of the magnetic field changes."

He told Newsweek that while some research indicates the weakening field could result in ozone depletion and an increase in UV radiation, he is skeptical these conditions could have led to extinctions: "UV can certainly cause skin cancers, but animals with fur should be well protected. And, I don't think mutations caused by UV will be passed down to offspring.

"I'm skeptical of the connection with Neanderthal extinction as well. However, what I could see being reasonable here is if the Neanderthal population was already reduced and stressed, then adding UV damage might contribute to that."

This article has been updated to include quotes from Brian Thomas.