Earth’s magnetic field is generated by the turbulent motion of molten nickel and iron in the planet’s outer core. Although this invisible shield feels permanent, it periodically weakens and reorganizes, causing the magnetic north and south poles to swap places. These events, known as Geomagnetic reversals, are recorded in rocks and ocean sediments, where tiny magnetic minerals preserve the direction of Earth’s field at the time they formed.
For decades, scientists believed that most reversals unfolded relatively quickly on geological timescales, typically completing in about 10,000 years. Over the past 170 million years, more than 540 such flips have occurred. However, new research led by a geoscientist from University of Utah, working with collaborators in France and Japan including Yuhji Yamamoto of Kochi University, challenges this long-held assumption. Their study reveals that some Geomagnetic reversals around 40 million years ago took dramatically longer—up to 70,000 years—reshaping scientific understanding of how Earth’s magnetic system behaves.
These findings emerged from sediment cores collected during a 2012 North Atlantic drilling campaign carried out under Integrated Ocean Drilling Program Expedition 342. The expedition targeted deposits from the Eocene Epoch, a period marked by major climate change. By drilling up to 300 meters beneath the seafloor off Newfoundland, researchers recovered layered sediments that act as time capsules, preserving magnetic signals grain by grain over millions of years.
As paleomagnetists, the team measured both the direction and strength of magnetization in these cores. Microscopic crystals of magnetite—formed by ancient microorganisms and carried in from continental dust—lock in the orientation of Earth’s magnetic field as sediments accumulate. Normally, a reversal appears as a relatively narrow transition between stable polarities. But one unusually thick, eight-meter interval showed a prolonged phase of unstable magnetism. Follow-up sampling at extremely fine spacing confirmed that this was not a quirk of sedimentation but a genuine record of two drawn-out reversals, one lasting about 18,000 years and another stretching to roughly 70,000 years.
These extended transitions matter because the magnetic field weakens significantly during reversals, reducing Earth’s protection from solar and cosmic radiation. According to co-author Peter Lippert, this diminished shielding could have influenced atmospheric chemistry, climate processes, and even biological evolution. Higher radiation levels may disrupt animal navigation, increase genetic mutation rates, and contribute to atmospheric erosion—effects that would be felt globally, especially at higher latitudes. In this sense, Geomagnetic reversals are not just deep-Earth phenomena; they may also play a subtle role in shaping life at the surface.
Importantly, computer models of Earth’s geodynamo—the churning outer core that generates the magnetic field—have long suggested that reversal durations should vary widely, with occasional exceptionally long events lasting up to 130,000 years. The new sediment evidence finally confirms these predictions in real geological records. Rather than following a uniform script, Geomagnetic reversals appear to be inherently unpredictable, with some flips unfolding slowly over tens of thousands of years. This discovery highlights a previously hidden complexity in Earth’s magnetic history and underscores how much remains to be learned about the planet’s dynamic interior.
https://phys.org/news/2026-02-earth-magnetic-field-flipping.html