Letter | Published:

Experimental determination of the electrical resistivity of iron at Earth’s core conditions

Nature volume 534, pages 9598 (02 June 2016) | Download Citation

Abstract

Earth continuously generates a dipole magnetic field in its convecting liquid outer core by a self-sustained dynamo action. Metallic iron is a dominant component of the outer core, so its electrical and thermal conductivity controls the dynamics and thermal evolution of Earth’s core1. However, in spite of extensive research, the transport properties of iron under core conditions are still controversial2,3,4,5,6,7,8,9. Since free electrons are a primary carrier of both electric current and heat, the electron scattering mechanism in iron under high pressure and temperature holds the key to understanding the transport properties of planetary cores. Here we measure the electrical resistivity (the reciprocal of electrical conductivity) of iron at the high temperatures (up to 4,500 kelvin) and pressures (megabars) of Earth’s core in a laser-heated diamond-anvil cell. The value measured for the resistivity of iron is even lower than the value extrapolated from high-pressure, low-temperature data using the Bloch–Grüneisen law, which considers only the electron–phonon scattering. This shows that the iron resistivity is strongly suppressed by the resistivity saturation effect at high temperatures. The low electrical resistivity of iron indicates the high thermal conductivity of Earth’s core, suggesting rapid core cooling and a young inner core less than 0.7 billion years old10. Therefore, an abrupt increase in palaeomagnetic field intensity around 1.3 billion years ago11 may not be related to the birth of the inner core.

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Acknowledgements

We thank H. Gomi for discussions and assistance with experiments. H. Ichikawa helped with the temperature distribution calculations. High-pressure experiments were conducted at BL10XU, SPring-8 (proposal numbers 2012B1131, 2012B1212, 2013B0080, 2014A0080, and 2014B0080).

Author information

Affiliations

  1. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan

    • Kenji Ohta
  2. Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan

    • Yasuhiro Kuwayama
  3. Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8550, Japan

    • Kei Hirose
  4. Laboratory of Ocean-Earth Life Evolution Research, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

    • Kei Hirose
  5. Center for Science and Technology under Extreme Conditions, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan

    • Katsuya Shimizu
  6. Japan Synchrotron Radiation Research Institute, 1-1-1 Koto, Sayo, Hyogo 679-5198, Japan

    • Yasuo Ohishi

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Contributions

K.O. designed the project. Y.K., K.H., K.S. and Y.O. supported the experiments. The manuscript was written by K.O. and K.H. and reviewed by all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Kenji Ohta.

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https://doi.org/10.1038/nature17957

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