An enduring mystery about Earth has been the age of its solid inner core. Plausible yet contrasting core thermal conductivity values lead to inner core growth initiation ages that span 2 billion years, from ~0.5 to >2.5 billion years ago. Palaeomagnetic data provide a direct probe of past core conditions, but heretofore field strength data were lacking for the youngest predicted inner core onset ages. Here we present palaeointensity data from the Ediacaran (~565 million years old) Sept-Îles intrusive suite measured on single plagioclase and clinopyroxene crystals that hosted single-domain magnetic inclusions. These data indicate a time-averaged dipole moment of ~0.7 × 1022 A m2, the lowest value yet reported for the geodynamo from extant rocks and more than ten times smaller than the strength of the present-day field. Palaeomagnetic directional studies of these crystals define two polarities with an unusually high angular dispersion (S = ~26°) at a low latitude. Together with 14 other directional data sets that suggest a hyper-reversal frequency, these extraordinary low field strengths suggest an anomalous field behaviour, consistent with predictions of geodynamo simulations, high thermal conductivities and an Ediacaran onset age of inner core growth.
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Data presented here are available in the Earthref (MagIC) database (earthref.org/MagIC/16534).
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Ohta, K., Kuwayama, Y., Hirose, K., Shimizu, K. & Ohishi, Y. Experimental determination of the electrical resistivity of iron at Earth’s core conditions. Nature 534, 95–98 (2016).
Konôpková, Z., McWilliams, R. S., Gómez-Pérez, N. & Goncharov, A. F. Direct measurement of thermal conductivity in solid iron at planetary core conditions. Nature 534, 99–101 (2016).
Tarduno, J. A. et al. Geodynamo, solar wind, and magnetopause 3.4 to 3.45 billion years ago. Science 327, 1238–1240 (2010).
Tarduno, J. A., Cottrell, R. D., Davis, W. J., Nimmo, F. & Bono, R. K. A Hadean to Paleoarchean geodynamo recorded by single zircon crystals. Science 349, 521–524 (2015).
O’Rourke, J. G. & Stevenson, D. J. Powering Earth’s dynamo with magnesium precipitation from the core. Nature 529, 387–389 (2016).
Badro, J., Siebert, J. & Nimmo, F. An early geodynamo driven by exsolution of mantle components from Earth’s core. Nature 536, 326–328 (2016).
Hirose, K. et al. Crystallization of silicon dioxide and compositional evolution of the Earth’s core. Nature 543, 99–102 (2017).
Driscoll, P. Simulating 2 Ga of geodynamo history. Geophys. Res. Lett. 43, 5680–5687 (2016).
Biggin, A. J. et al. Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation. Nature 526, 245–248 (2015).
Smirnov, A. V., Tarduno, J. A., Kulakov, E. V., McEnroe, S. A. & Bono, R. K. Palaeointensity, core thermal conductivity and the unknown age of the inner core. Geophys. J. Int. 205, 11901195 (2016).
Driscoll, P. & Bercovici, D. On the thermal and magnetic histories of Earth and Venus: influences of melting, radioactivity, and conductivity. Phys. Earth Planet. Inter. 236, 36–51 (2014).
Labrosse, S. Thermal evolution of the core with a high thermal conductivity. Phys. Earth Planet. Inter. 247, 36–55 (2015).
Nimmo, F. in Treatise on Geophysics 2nd edn (ed. Schubert, G.) 201–219 (Elsevier, Amsterdam, 2015).
Bono, R. K. & Tarduno, J. A. A stable Ediacaran Earth recorded by single silicate crystals of the ca. 565 Ma Sept-Îles intrusion. Geology 43, 131–134 (2015).
Tarduno, J. A., Cottrell, R. D. & Smirnov, A. V. The paleomagnetism of single silicate crystals: recording the geomagnetic field during mixed polarity intervals. Rev. Geophys. 44, RG1002 (2006).
Tarduno, J. A. Geodynamo history preserved in single silicate crystals: origins and long-term mantle control. Elements 5, 217–222 (2009).
Dunlop, D. J. & Özdemir, Ö. Rock Magnetism: Fundamentals and Frontiers (Cambridge Univ. Press, Cambridge, 1997).
Smirnov, A. V., Kulakov, E. V., Foucher, M. S. & Bristol, K. E. Intrinsic paleointensity bias and the long-term history of the geodynamo. Sci. Adv. 3, e1602306 (2017).
Tarduno, J. A., Cottrell, R. D., Watkeys, M. K. & Bauch, D. Geomagnetic field strength 3.2 billion years ago recorded by single silicate crystals. Nature 446, 657–660 (2007).
Selkin, P. A., Gee, J. S. & Tauxe, L. Nonlinear thermoremanence acquisition and implications for paleo-intensity data. Earth Planet. Sci. Lett. 256, 81–89 (2007).
Feinberg, J. M., Scott, G. R., Renne, P. R. & Wenk, H.-R. Exsolved magnetite inclusions in silicates: features determining their remanence behavior. Geology 33, 513–516 (2005).
Tarduno, J. A. & Cottrell, R. D. Dipole strength and variation of the time-averaged reversing and nonreversing geodynamo based on Thellier analyses of single plagioclase crystals. J. Geophys. Res. 110, B11101 (2005).
Shcherbakova, V. V. et al. Was the Devonian geomagnetic field dipolar or multipolar? Palaeointensity studies of Devonian igneous rocks from the Minusa Basin (Siberia) and the Kola Peninsula dykes, Russia. Geophys. J. Int. 209, 1265–1286 (2017).
Tarduno, J. A., Blackman, E. G. & Mamajek, E. E. Detecting the oldest geodynamo and attendant shielding from the solar wind: implications for habitability. Phys. Earth Planet. Inter. 233, 68–87 (2014).
Shcherbakova, V., Bakhmutov, V., Shcherbakov, V. & Zhidkov, G. Extremely low palaeointensities in the Neoproterozoic obtained on volcanic rocks from the Ukrainan shield. Geophys. Res. Abstr. 20, EGU2018-11598 (2018).
Halls, H. C., Lovette, A., Hamilton, M. & Söderlund, U. A paleomagnetic and U–Pb geochronology study of the western end of the Grenville dyke swarm: rapid changes in paleomagnetic field direction at ca. 585 Ma related to polarity reversals? Precambrian Res. 257, 137–166 (2015).
Bazhenov, M. L. et al. Late Ediacaran magnetostratigraphy of Baltica: evidence for magnetic field hyperactivity? Earth Planet. Sci. Lett. 435, 124–135 (2016).
Aubert, J., Labrosse, S. & Poitou, C. Modelling the palaeo-evolution of the geodynamo. Geophys. J. Int. 179, 1414–1428 (2009).
Landeau, M., Aubert, J. & Olson, P. The signature of inner-core nucleation on the geodynamo. Earth Planet. Sci. Lett. 465, 193–204 (2017).
Doglioni, C., Pignatti, J. & Coleman, M. Why did life develop on the surface of the Earth in the Cambrian? Geosci. Front. 7, 865–873 (2016).
Meert, J. G., Levashova, N. M., Bazhenov, M. L. & Landing, E. Rapid changes of magnetic field polarity in the late Ediacaran: linking the Cambrian evolutionary radiation and increased UV-B radiation. Gondwana Res. 34, 149–157 (2016).
Herzberg, C., Condie, K. & Korenaga, J. Thermal history of the Earth and its petrological expression. Earth Planet. Sci. Lett. 292, 79–88 (2010).
O’Rourke, J. G., Korenaga, J. & Stevenson, D. J. Thermal evolution of Earth with magnesium precipitation in the core. Earth Planet. Sci. 458, 263–272 (2017).
Coe, R. S. The determination of paleo-intensities of the Earth’s magnetic field with emphasis on mechanisms which could cause non-ideal behavior in Thellier’s method. J. Geomag. Geoelectr. 19, 157–179 (1967).
Shaar, R., Tauxe, L. & Thellier, G. U. I. An integrated tool for analyzing paleointensity data from Thellier-type experiments. Geochem. Geophys. Geosys. 14, 677–692 (2013).
Coe, R. S., Grommé, S. & Mankinen, E. A. Geomagnetic paleointensities from radiocarbon-dated lava flows on Hawaii and the question of the Pacific nondipole low. J. Geophys. Res. 83, 1740–1756 (1978).
Veitch, R. J., Hedley, I. G. & Wagner, J.-J. An investigation of the intensity of the geomagnetic field during Roman times using magnetically anisotropic bricks and tiles. Arch. Sci. 37, 359–373 (1984).
Riisager, P. & Riisager, J. Detecting multidomain magnetic grains in Thellier palaeointensity experiments. Phys. Earth Planet. Inter. 125, 111–117 (2001).
We thank G. Kloc for the sample preparation, B. L. McIntyre and R. Wiegandt for the electron microscope analyses and T. Zhou for magnetic hysteresis measurements. This work was supported by the National Science Foundation (grant nos EAR1520681 and EAR1656348 to J.A.T.).
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Nature Geoscience (2019)