Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo

 View ORCID ProfileJohn A. Tarduno,  View ORCID ProfileRory D. Cottrell,  View ORCID ProfileRichard K. Bono,  View ORCID ProfileHirokuni Oda,  View ORCID ProfileWilliam J. Davis,  View ORCID ProfileMostafa Fayek,  View ORCID ProfileOlaf van ’t Erve,  View ORCID ProfileFrancis Nimmo,  View ORCID ProfileWentao Huang,  View ORCID ProfileEric R. Thern,  View ORCID ProfileSebastian Fearn, Gautam Mitra,  View ORCID ProfileAleksey V. Smirnov, and  View ORCID ProfileEric G. Blackman

PNAS February 4, 2020 117 (5) 2309-2318; first published January 21, 2020 https://doi.org/10.1073/pnas.1916553117

1. Edited by Lisa Tauxe, University of California San Diego, La Jolla, CA, and approved December 12, 2019 (received for review September 24, 2019)

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Significance

The age and early history of Earth’s geomagnetic field can provide insight into the evolution of the core and atmosphere. But measurement of Hadean zircons—the oldest known terrestrial materials—and the determination of the antiquity of their magnetizations are amongst the most challenging endeavors in paleomagnetism. New paleomagnetic, electron microscope, geochemical, and paleointensity data indicate the presence of primary magnetite inclusions in select zircons. These data support the presence of the geomagnetic field, and associated shielding of the atmosphere from the solar wind, ∼4.2 billion years ago. A relatively strong field recorded by these zircons at ∼4 billion years ago may be a signal that chemical precipitation in the core was powering the geodynamo.

Abstract

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.