Carbon-depleted outer core revealed by sound velocity measurements of liquid iron-carbon alloy

Yoichi Nakajima, Saori Imada, Kei Hirose, Tetsuya Komabayashi, Haruka Ozawa, Shigehiko Tateno, Satoshi Tsutsui, Yasuhiro Kuwayama, Alfred Q.R. Baron

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)


The relative abundance of light elements in the Earth's core has long been controversial. Recently, the presence of carbon in the core has been emphasized, because the density and sound velocities of the inner core may be consistent with solid Fe7C3. Here we report the longitudinal wave velocity of liquid Fe84C16 up to 70GPa based on inelastic X-ray scattering measurements. We find the velocity to be substantially slower than that of solid iron and Fe3C and to be faster than that of liquid iron. The thermodynamic equation of state for liquid Fe84C16 is also obtained from the velocity data combined with previous density measurements at 1 bar. The longitudinal velocity of the outer core, about 4% faster than that of liquid iron, is consistent with the presence of 4-5 at.% carbon. However, that amount of carbon is too small to account for the outer core density deficit, suggesting that carbon cannot be a predominant light element in the core.

Original languageEnglish
Article number8942
JournalNature communications
Publication statusPublished - Nov 24 2015
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Physics and Astronomy(all)


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