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Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth’s Hadean liquid iron core.
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This content will become publicly available on January 7, 2027
Geomagnetic Variability in a Post‐Superchron Geodynamo: Insights From the Deccan Traps
Studying long-term geomagnetic field behavior is crucial for understanding Earth's evolution, as field variability reflects processes in the planet's deep interior. One key question concerns the relationship between field strength and polarity reversal frequency, particularly during the Cretaceous Normal Superchron (CNS), a prolonged interval without reversals. We present new paleomagnetic and paleointensity data from the Deccan Traps, emplaced shortly after the CNS potentially recording the geodynamo's transition back to a reversing state. Sixteen reliable paleointensity estimates were obtained from three sites and have Quality of Paleointensity (QPI) scores of seven to eight. To evaluate selection criteria, results were compared using SELCRIT2, Thellier Tool A, MI-CRIT.A1, and PICRIT03. SELCRIT2 proved too permissive, whereas MI-CRIT.A1 most effectively excluded potentially biased data. Site mean Virtual Dipole Moments decrease stratigraphically from 7.0 ± 0.8 × 1022 Am2 at the base to 5.5 ± 0.4 × 1022 Am2 at the top of our sampled section. These values are higher than prior ∼66 Ma estimates which meet QPI ≥ 3 criteria and are instead more consistent with data satisfying the stricter prioritized QPI subset (QAGE + QALT + QMD). Together with existing records and model observations, our results suggest that the geomagnetic field was weaker and less variable after the CNS, supporting a closer link between reversal frequency and intensity range than absolute strength alone. Nonetheless, even rigorously filtered data sets may retain biases, complicating interpretations of this enigmatic period. Our study underscores the need for stringent selection criteria in paleointensity research.
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- PAR ID:
- 10672364
- Publisher / Repository:
- Journal of Geophysical Research: Solid Earth
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 131
- Issue:
- 1
- ISSN:
- 2169-9313
- Page Range / eLocation ID:
- e2025JB033124
- Format(s):
- Medium: X
- Associated Dataset(s):
- View Associated Dataset(s) >>
- Sponsoring Org:
- National Science Foundation
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