Researchers may have found the ages that hide undiscovered geomagnetic reversals using statistical analysis
JSPS Research Fellow Yutaka Yoshimura
Faculty of Social and Cultural Studies
In everyday life, we can easily tell whether objects are packed tightly (high density) or spread out sparsely (low density) just by looking at them. But when dealing with time-series event data, scattering along a timeline, it is not as straightforward to objectively identify when the density is high or low. A statistical method called kernel density estimation is useful. By assigning a probability to each data point and overlaying these distributions, the method provides a smooth estimate of how event density changes over time. It is particularly effective for analyzing the timing of geomagnetic reversals.
In geophysics, researchers have compiled records of geomagnetic polarity reversals and examined how their frequency varies over time. Reversals cluster during certain intervals and become very rare during others. These differences are thought to reflect variations in heat flow across the core–mantle boundary, which influence the geodynamo that generates Earth’s magnetic field. Periods with high reversal density provide abundant magnetic signatures preserved in land and seafloor rocks and sediments, enabling more precise estimates of past plate positions, fossil ages, and the timing of environmental changes. In contrast, periods with very low reversal density offer fewer dating markers, making reconstructions of Earth’s ancient history more challenging.
An international research team, including Kyushu University and other institutions across Japan, the Republic of Korea, and the United States, analyzed the latest reversal timing dataset (GPTS2020). The researchers applied an adaptive-bandwidth kernel density estimation (AKDE) method to estimate reversal frequency while accounting for the uneven temporal spacing of events. With improved parameter selection, they estimated variations in reversal frequency with higher temporal resolution.
The researchers thus identified four distinct dips in the new reversal frequency model following the Cretaceous Normal Superchron, which lasted from approximately 121 to 83 million years ago. This finding supports the interpretation that smoother, long-term variations more closely represent the underlying behavior of the geodynamo. It also indicates that the four periods showing dips in reversal frequency may contain missing reversals.
The researchers conclude that dips in geomagnetic reversal frequency are promising candidates for future investigations aimed at identifying potentially missing reversals. Additionally, this research contributes to improved understanding of the long-term behavior of Earth’s magnetic field and the dynamics of the deep Earth.
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Yutaka Yoshimura, JSPS Research Fellow
Faculty of Social and Cultural Studies
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