Earth’s early magnetic field

A study finds evidence of magnetism in some of Earth’s oldest minerals that suggests a strong early magnetic field around 4 billion years ago. The development of Earth’s magnetic field protected the planet from the detrimental effects of solar wind. However, evidence of the early magnetic field during the Hadean eon is sparse, given that few minerals remain from that eon and many have undergone later metamorphism that reset the magnetic clock. John A. Tarduno and colleagues conducted magnetic paleointensity studies on zircon crystals from the Jack Hills of Western Australia, dated to between 3.2 and 4.2 billion years ago. The authors found and analyzed magnetite crystals within the zircons, from which magnetic data could be extrapolated. The results suggest that a magnetic field, with associated shielding from the solar wind, was likely in place by 4.2 billion years ago. Further, the data suggest that the magnetic field was relatively strong between 4.1 and 4 billion years ago. According to the authors, the strong magnetic field was likely due to an internal geodynamo powered by the precipitation of minerals in the core after several million years of cooling.

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Article #19-16553: “Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo,” by John A. Tarduno et al.

MEDIA CONTACT: John A. Tarduno, University of Rochester, NY; tel: 585-275-5713; e-mail: <

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