Evidence for a very-long-term trend in geomagnetic secular variation

Abstract

The Earth’s inner core is believed to inhibit rapid fluctuations in the geomagnetic field from developing into full polarity reversals1,2. Consequently, during the Precambrian, the smaller size of the inner core might suggest that polarity reversals could occur more readily. It is therefore surprising that there are indications that reversals were rare during this period3,4. Here we use new and existing palaeomagnetic data from three continents to examine the stability of the Earth’s magnetic field from 2.82 to 2.45 billion years ago. We show that, on average, geomagnetic secular variation (the field variations produced by normal geodynamo action) during the late Archaean and early Proterozoic was different from that of the past 200 million years; specifically, the apparent variability of the geomagnetic pole as viewed at low and mid-latitudes was reduced relative to the past 200 million years. According to both dynamo simulations4 and more recent palaeomagnetic field observations5, the observed pattern of secular variation suggests a lower frequency of polarity reversals 2.5 billion years ago. This may imply that the geodynamo is becoming progressively less stable over long timescales, consistent with some numerical simulations6,7, possibly as a result of changing outer-core geometry that has accompanied inner-core growth.

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Figure 1: VGP dispersion plots for the periods 2.45–2.82 Gyr and 0–5 Myr.
Figure 2: Comparison of PSV in the periods 2.45–2.82 Gyr and 0–195 Myr.

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Acknowledgements

This research was undertaken with funding provided by the Netherlands Science Foundation (NWO) and conducted under the programme of the Vening Meinesz Research School of Geodynamics (VMSG).

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Contributions

A.J.B. undertook the palaeosecular variation analyses and provided the interpretation. G.H.M.A.S. obtained the newly reported data from the Pilbara Craton and undertook PSV analyses on these. C.G.L. initiated the project and advised and assisted throughout.

Corresponding author

Correspondence to Andrew J. Biggin.

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Supplementary Information

Supplementary figures S1-S4 and table S1 (PDF 521 kb)

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Biggin, A., Strik, G. & Langereis, C. Evidence for a very-long-term trend in geomagnetic secular variation. Nature Geosci 1, 395–398 (2008). https://doi.org/10.1038/ngeo181

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