AI Insight
Malinverno and Meyers have developed a refined Geomagnetic Polarity Time Scale (GPTS) covering 33 to 83 million years ago by integrating three independent dating methods: marine magnetic anomalies, radioisotopic dating, and astrochronology. Using a Bayesian framework and Monte Carlo approach, they created a more precise time scale that equally weights all three methods while minimizing assumptions about seafloor spreading rate changes. The resulting MM26 time scale provides quantified uncertainties and demonstrates that astrochronological methods can produce reliable high-resolution dating even for geological periods lacking marine magnetic anomaly data.
Why it matters
An accurate geomagnetic polarity time scale is fundamental for dating geological and biological events and calculating their rates of change throughout Earth's history. This improved methodology provides a template for constructing more precise time scales across other geological periods, enabling better understanding of past climate changes, evolutionary events, and Earth system processes.
Understand the Science
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Solid Earth
The Geomagnetic Polarity Time Scale (GPTS), the sequence of normal and reverse polarity chrons with absolute ages assigned to them, is a foremost means to date geological and biological processes and assess their rates of chance. Evidently for correct conclusions, the GPTS must be as precise and accurate as possible. Recent GPTS versions rely heavily on astrochronologically derived chron durations with radioisotopic ages and ocean floor magnetic anomalies having a secondary role only.
Here, starting from a Bayesian formulation, Malinverno and Meyers [2026] construct a refined time scale for the age range between 33 and 83 million years ago by integrating these three approaches while keeping them on the same level, under the premise of minimizing rate changes in sea floor spreading. Time scale uncertainties are now quantified by a Monte Carlo approach—an important asset. The study is a template for time scale construction and indicates ways to further refine this time scale. Also, it inherently illustrates that high-resolution time scales with astrochronologically derived durations can be faithful for periods for which no marine magnetic anomalies do exist (i.e. most of the geological record), given the relatively modest differences between the new time scale and CENOGRID.
Citation: Malinverno, A., & Meyers, S. R. (2026). A Late Cretaceous-Eocene Geomagnetic Polarity Time Scale (MM26) that combines marine magnetic anomaly records, radioisotopic dates, and astrochronology. Journal of Geophysical Research: Solid Earth, 131, e2025JB033130. https://doi.org/10.1029/2025JB033130
—Mark Dekkers, Editor, JGR: Solid Earth
Text © 2026. The authors. CC BY-NC-ND 3.0
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Source: The Geomagnetic Polarity Time Scale Revisited Once Again