Earth’s magnetic field flipped rapidly across a mass extinction about 261 million years ago
image:
(a) Polarity reversal frequency (blue line) and Paleointensity data. Dark-pink symbols with error bars illustrate mean paleointensity values calculated within age clusters. IR: Illawarra Reversal. (b) Volcanic activities. Dark red denotes the major phase of large igneous provinces (LIPs). Grey bars illustrate the silicic LIPs (SLIP). (c) Eustatic sea-level fluctuations and Pangea supercontinent configuration. (d) Carbon isotope profile. (e) Species diversity trends. EGME and EPME: End-Guadalupian mass extinction and End-Permian mass extinctions, respectively. T: Triassic Period. C: Carboniferous Period.
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Earth’s magnetic field is generated by the convection of liquid iron in the outer core. It forms a protective shield that deflects most solar wind and galactic cosmic rays, limiting ionization in the upper atmosphere and helping maintain the ozone layer that screens life from ultraviolet radiation. Over geologic time the field reverses polarity many times, but the rate of those reversals is not constant. Long stretches of stability alternate with intervals of rapid flipping, and those changes are thought to reflect variations in heat flow across the core-mantle boundary.
About 261 million years ago, during the middle-late Permian, Earth was already under extremely chaos. The supercontinent Pangea was fully assembled, sea levels were unusually low, and massive volcanic eruptions were releasing gases that warmed the climate and disrupted ocean chemistry. Against this backdrop, a new study from the Fengshan section in southern China shows that the planet’s magnetic field was also in turmoil.
For tens of millions of years during the late Carboniferous and much of the Permian, Earth’s magnetic field stayed a single reversed polarity. That long quiet interval, known as the Kiaman Superchron, ended near 265 million years ago. What followed, according to a new high-resolution study of the Fengshan section in South China, was one of the most restless stretches of geomagnetic behavior yet measured.
Across a 3.75-million-year interval from about 262.5 to 258.75 million years ago, researchers recovered 29 distinct magnetic polarity zones. In the roughly 1.7 million years immediately before the end-Guadalupian extinction, the reversal rate climbed to approximately 11 reversals per million years—an order of magnitude higher than the long-term average in the geologic record. After the extinction, the field settled into a quieter pattern for a few million years.
The record comes from continuous shallow-water limestones that were deposited near the paleo-equator. Of more than 870 oriented specimens, 309 yielded stable, dual-polarity directions that survived rigorous demagnetization and reliability tests. Biostratigraphy, cyclostratigraphy, and radiometric anchors pin the hyperactive interval tightly against the extinction horizon near 261 million years ago.
The end-Guadalupian event itself is often overshadowed by the larger end-Permian mass extinction that followed roughly ten million years later, yet it was already severe: reef systems collapsed, many marine invertebrates declined sharply, and terrestrial ecosystems showed clear disruption. Conventional explanations center on the Emeishan large igneous province, global sea-level fall linked to Pangea’s assembly, and resulting ocean and climate stress. The new magnetostratigraphic data raise the possibility that an unstable geodynamo added another, less familiar pressure.
A more disordered or weaker field would have reduced the magnetosphere’s ability to deflect galactic cosmic rays and solar particles. Increased ionization in the upper atmosphere can erode ozone and raise surface ultraviolet flux—effects that have been documented, through pollen malformations and UV-protective compounds, at the later end-Permian crisis. Whether similar processes operated around 261 million years ago is not yet clear; the authors note that direct evidence is still limited and that LIP-derived halogens remain a plausible alternative or complementary driver of any ozone loss.
The geomagnetic instability itself is interpreted as a surface expression of changes deep in the Earth. After the long Kiaman stability, descending lithospheric slabs associated with the final assembly of Pangea may have reached the core-mantle boundary, locally increasing heat extraction from the core and introducing lateral variations in heat flux. Geodynamo simulations indicate that such heterogeneity can promote frequent reversals, although the models operate far from fully Earth-like conditions and remain sensitive to parameter choices.
The study does not claim that magnetic-field chaos caused the extinction. It documents a striking temporal coincidence and outlines a physically plausible pathway by which deep-Earth processes could have amplified surface environmental stress. Testing that pathway will require better paleointensity records across the same interval, tighter age constraints, and coupled atmospheric modeling. In the meantime, the Fengshan polarity sequence supplies one of the clearest windows yet into how the planet’s magnetic field behaved during a critical chapter of the late Paleozoic.
The research was led by scientists at the Institute of Geology and Geophysics, Chinese Academy of Sciences, with collaborators from Utrecht University, BOKU University, Nanjing University, and other institutions. It was supported by the National Natural Science Foundation of China.
