Every so often, the magnetic north and south poles swap places in what are called geomagnetic reversals, and the record of these flips is preserved in rocks and sediments, including those from the ocean floor. These reversals don’t happen suddenly, but over several thousand years, where the magnetic field fades and wobbles while the two poles wander and finally settle in the opposite positions of the globe.
Over the past 170 million years, the magnetic poles have reversed 540 times, with the reversal process typically taking around 10,000 years to complete each time, according to years of research. Now, a new study by a University of Utah geoscientist and colleagues from France and Japan has upended this scenario after documenting instances 40 million years ago where the process took far longer to complete, upwards of 70,000 years. These findings offer a new perspective on the geomagnetic phenomenon that envelops our planet and shields it from solar radiation and harmful particles from space.
Extended periods of reduced geomagnetic shielding likely influenced atmospheric chemistry, climate processes and the evolution of living organisms, according to co-author Peter Lippert, an associate professor in the U Department of Geology & Geophysics.
“The amazing thing about the magnetic field is that it provides the safety net against radiation from outer space, and that radiation is observed and hypothesized to do all sorts of things. If you are getting more solar radiation coming into the planet, it’ll change organisms’ ability to navigate,” said Lippert, who heads the Utah Paleomagnetic Center. “It’s basically saying we are exposing higher latitudes in particular, but also the entire planet, to greater rates and greater durations of this cosmic radiation and therefore it’s logical to expect that there would be higher rates of genetic mutation. There could be atmospheric erosion.”
The results appear in Nature Communications Earth & Environment. The lead author is Yuhji Yamamoto of Japan’s Kochi University.
“This finding unveiled an extraordinarily prolonged reversal process, challenging conventional understanding and leaving us genuinely astonished,” Yamamoto wrote in a summary posted by Springer Nature.
Yamamoto and Lippert worked together on a 2012 drilling expedition in the North Atlantic that was investigating climate change during the Eocene Epoch, 56 to 34 million years ago. The two-month trip was facilitated by the International Ocean Discovery Program’s Expedition 342. The team drilled off the coast of Newfoundland in the North Atlantic, extracting sediment cores, layered time capsules built grain by grain over millions of years, from up to 300 meters below the sea floor.