Earth’s Magnetic Field Flips Much More Frequently Than Thought

October 3, 2019

The planet’s magnetic poles swapped places at an astounding rate about 500 million years ago, which offers clues to core formation and hints at the effects on early life.

Yves Gallet balanced on a steep rocky slope in northeast Siberia, a turquoise river leisurely wending across the undulating landscape that sprawled below. But Gallet, of France’s Institut de Physique du Globe de Paris, had his face turned toward the rocks with one goal in mind: deciphering the history of Earth’s magnetic field.

This protective bubble shields Earth from radiation that’s constantly streaming from the sun. In the planet’s 4.6-billion-year history, the field has frequently flipped, swapping magnetic north and south, and some research suggests that another flip may be on the geological horizon. While fears of a looming geomagnetic apocalypse are overblown, a magnetic reversal could have many damaging impacts, from increased radiation exposure to technological disruptions, which makes understanding these historic flips more than just a scientific curiosity. (Learn more about what might happen when the magnetic poles flip.)

Now, Gallet and his colleagues have uncovered evidence of one of the highest rates of field reversals yet recorded. During this stunningly chaotic time, detailed in a recent publication in Earth and Planetary Science Letters, the planet experienced 26 magnetic pole reversals every million years—more than five times the rate seen in the last 10 million years.

The result joins a mounting set of evidence that suggests the planet’s magnetic field is capable of flipping more frequently than once thought possible, says Joseph Meert, a paleomagnetist at the University of Florida who was not part of the study team. Such research is slowly filling in Earth’s spotty magnetic record, which could help scientists better understand the timing and reason behind these geologic gymnastics—and may even hint at the effects ancient periods of hyperactivity had on early life.

Earth’s restless poles

Earth’s magnetic field is charged by the churn of the molten iron and nickel of our planet’s outer core, some 1,800 miles below the surface. Over the years, the field’s turns and tumbles have been captured by iron-rich minerals attuned to magnetic influences, which can become trapped in place as sedimentary rocks form or lava cools, like tiny compass needles frozen in time.

Based on this rocky record, our poles haven’t switched places in some 780,000 years, but they’ve been restless in the past, reversing every 200,000 years or so. There are also prolonged periods when the poles largely stayed put, such as a 40-million-year block of time during the Jurassic period some 100 million years ago.

How fast can these reversals get? For answers, Gallet and his colleagues ventured by helicopter, inflatable raft, and foot to precarious cliffs that date to a sparsely sampled period in the Middle Cambrian, some 500 million years ago. The sands that built this region were laid down in what was once a warm, shallow sea, with magnetic minerals trapped in place as sediments drifted to the quiet ocean floor and compacted to form new rock layers.

Gallet and his colleagues first visited the site in the early 2000s, collecting around 119 samples from the nearly vertical face of rock. This work revealed a period during the Middle Cambrian that saw at least six to eight field reversals every million years.

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