Japanese researchers say they are closing in on the mystery of Earth’s “missing” geomagnetic polarity reversals, identifying where they believe scientists should look for evidence of their unusual absence.
Over long timescales, Earth’s magnetic poles periodically switch in events known as geomagnetic polarity reversals, which mark major chapters in the planet’s magnetic history. The interval between these reversals is called a chron, and new research published in Geophysical Research Letters suggests more of these events may have occurred than are currently confirmed.
Missing Geomagnetic Polarity Reversals
Geological materials—including rocks, sediments, and marine magnetic anomalies—preserve the history of Earth’s many polarity reversals. Researchers are particularly interested in “missing” reversals: events that likely occurred but for which there is no clear evidence yet.
“Some ‘missing’ reversals, not yet registered in the reversal history, are discovered from the Ethiopian flood basalts,” lead author Yutaka Yoshimura of Kyushu University told The Debrief. “They are called the Lima-Limo reversals. Also, the geomagnetic excursions, which are failed geomagnetic polarity changes, may be candidate of the ‘missing’ reversals. The 24 geomagnetic excursions may occurred in the past 773,000 years according to Singer et al.”
Scientists attribute reversals to long-term changes in heat flow across the core-mantle boundary, which affect the geodynamo that generates Earth’s magnetic field.
Hunting for Geomagnetic Polarity Reversals
Taken together, these reversals form the Geomagnetic Polarity Time Scale (GPTS). Very short intervals present challenges because their brief duration can fall below the resolution limits of geological records. Using GPTS2020—the most recent reversal timing dataset—the team examined how reversal frequency has changed over time.
Researchers applied a technique known as kernel density estimation to determine whether events cluster closely on a timeline or are more widely spaced. Each data point is assigned a probability distribution, and overlapping distributions reveal how event density shifts across geological time. The method is especially useful when studying long-term reversal records.
Earlier studies using this approach suggested that about 155 million years ago, near the onset of the Cretaceous Normal Superchron, reversals steadily declined. After the superchron ended around 83 million years ago, reversal frequency began increasing again.
Locating Polarity Reversals
Geodynamo simulations show that patterns of heat flow at the core-mantle boundary influence reversal frequency. Over tens of millions of years, mantle convection and true polar wander gradually alter this heat flow, leading scientists to expect a continuously changing reversal rate.
By analyzing reversal timing data, the researchers identified dense clusters and sparse periods when few reversals occurred. During high-density intervals, abundant data points allow more precise estimates of environmental changes, plate movements, and fossil ages based on magnetic signatures in rock and sediment.
Short intervals missing from the geological record appear as dips in the team’s new frequency model. Although these low-density periods lack continuous dating markers and are therefore harder to analyze, their absence still offers clues about Earth’s interior at the time.
Importantly, the model achieved higher resolution for these short intervals, revealing four distinct dips after the Cretaceous Normal Superchron. The team proposes that these gaps likely contain the missing geomagnetic polarity reversals and that the findings support the standard geodynamo explanation for reversals.
Magnetic Dating
Identifying these missing reversals could improve the dating of ancient geological materials.
“Geologists and geophysicists have developed and refined the Geomagnetic Polarity Time Scale (GPTS) as a geochronologic ‘ruler’ for magnetic dating,” Yoshimura said. “Therefore, magnetic reversals are the key layers to correlate the geomagnetic reversal signals recorded in oceanic plates and subaerial/submarine strata (including fossils and paleo-environmental events) to GPTS.”
“To further improve the accuracy and resolution of magnetic dating, it is essential to identify lava flows that erupted during the specific time intervals of interest and to conduct intensive paleomagnetic rock sampling on those units,” Yoshimura adds.
“This targeted strategy enables high-precision constraints on reversal timing and geomagnetic field behavior,” he says. “Such an approach has been central to our work in Ethiopia, where systematic sampling of well-preserved volcanic sequences has helped refine the temporal framework of geomagnetic reversals.”
As scientists continue reconstructing Earth’s geological past, each discovery informs the next. By identifying where to search for missing reversals, the team’s work may refine magnetic dating and provide researchers with a more precise tool for studying the planet’s deep history.
The paper, “Missing Geomagnetic Reversals in the Geomagnetic Reversal History,” appeared in Geophysical Research Letters on February 23, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.