The Earth’s magnetic field does more than just cause auroral light shows. Could it play a role in extinctions, too?
(NASA Astronaut Jack Fischer, ISS Expedition 52)
Lessons from the Laschamps Excursion 42,000 years ago
After studying the reversal of Earth’s magnetic pole known to have occurred 42,000 years ago, a science team led by Alan Cooper from the South Australian Museum in Adelaide, Australia concludes that the event had significant environmental repercussions, especially at lower and mid-latitudes. That time period, known as the Laschamps Excursion, had anomalously high radiocarbon concentrations in the atmosphere, which were linked to a higher influx of radiation. When the reversal occurred, within a span of about 1,000 years, Earth’s magnetic field weakened drastically and the magnetic North and South Poles flipped, temporarily leaving surface-dwelling organisms largely unprotected from high influxes of both ionic and ultraviolet radiation.
Previous studies had not found much of an environmental impact from the flip. But that conclusion was based primarily on ice cores from Greenland and Antarctica, which biased it toward higher latitudes. Cooper and his colleagues took more representative samples from all over the world, including from tree rings in New Zealand. They conclude that the magnetic reversal was in fact related to the extinction of a large fraction of large animals at the time, as well as the disappearance of the Neanderthals and even the appearance of cave art.
If the connection with mass extinctions is true, it’s a cause for concern. Earth’s magnetic field has weakened nearly 10 percent in the last 200 years, and the position of the magnetic North Pole has changed quite a bit. A magnetic reversal may be imminent. One can only imagine what trouble such an event could cause, with more solar and cosmic radiation hitting Earth’s surface. Potentially, we could see an increase in cancer rates, environmental disturbances, and the failure of power grids. Do we need to worry?
Yes and no. Yes, because our energy supply is increasingly fragile (see the recent effects of icy weather on Texas’s power grid), and much of our communication is based on satellites. If those are knocked out by solar storms, the effect on society could be substantial. No GPS, no social media, electrical power outages. Do I need to go on?
No, because a reversal may not necessarily have a big environmental impact after all. There have been other periods of magnetic weakening and reversals—the last one was 34,000 years ago—with apparently little effect, judging from the fossil record. During the Laschamps Excursion, or Adams Event as the authors call it, Earth was still in the grips of an ice age, with much of Europe and North America under glaciers. The Sun’s activity also was much lower at that time—a so-called Grand Solar Minimum, which happens periodically. So any extinction that occurred during that period may have been more due to the ice age than the magnetic reversal. Or maybe it was a combined effect. Humans may have retreated to caves because of both the cold and the higher radiation levels, with cold probably being a more important motivating factor.
I also don’t see how the Neanderthal extinction would be related to the environmental stress 42,000 years ago. If anything, Neanderthals, with their bulkier bodies, should have been more cold-adapted than Homo sapiens, who originated from East Africa. Not to mention that recent research shows that the Neanderthals did not actually go extinct during that time period.
There’s no doubt that higher radiation levels would impact the biosphere, but probably more on the individual rather than the species level. That’s true for humans, too. But our greatest vulnerability may lie in our technology, on which our society has become so dependent.
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