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Light elements in the Earth’s core

  • Review Article
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From Nature Reviews Earth & Environment

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Abstract

Constraining the core’s composition is essential for understanding Earth accretion, core formation and the sustainment of Earth’s magnetic field. Earth’s outer and inner core exhibit a density deficit relative to pure iron, attributed to the presence of substantial amounts of low atomic number ‘light’ elements, such as sulfur, silicon, oxygen, carbon and hydrogen. However, owing to its inaccessibility, estimates of core composition can only be indirectly obtained by matching results from high-pressure experiments and theoretical calculations with seismic observations. In this Review, we discuss the properties and phase relations of iron alloys under high-pressure and high-temperature conditions relevant to the Earth’s core. We synthesize mineral physics data with cosmochemical and geochemical estimates to give the likely range of compositions for the outer (Fe + 5% Ni + 1.7% S + 0–4.0% Si + 0.8–5.3% O + 0.2% C + 0–0.26% H by weight) and inner (Fe + 5% Ni + 0–1.1% S + 0–2.3% Si + 0–0.1% O + 0–1.3% C + 0–0.23% H by weight) core. While the exact composition of the core remains unknown, tighter constraints on core temperature and better connections between the solid inner core and the liquid outer core compositions will help narrow the range of potential light element compositions.

Key points

  • Constraining the light element composition of the core has profound implications for understanding Earth’s building blocks, accretion history, core formation and evolution processes, as well as present-day core temperature and dynamics.

  • The nature and concentrations of light elements have been hotly debated since the 1950s, but advances in mineral physics and cosmochemical and geochemical estimates suggest that the likely range of liquid outer core composition is: Fe + 5% Ni + 1.7% S + 0–4.0% Si + 0.8–5.3% O + 0.2% C + 0–0.26% H by weight.

  • Ab initio molecular dynamics simulations have shown that the compositional range of alloys that satisfy the seismic constraints for the solid inner core is: Fe + 5% Ni + 0–1.1% S + 0–2.3% Si + 0–0.1% O + 0–1.3% C + 0–0.23% H by weight.

  • Crystallization of oxides and metal near the surface and centre of the core, respectively, could drive liquid core convection, thus, enabling the generation and maintenance of the Earth’s magnetic field.

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Fig. 1: Formation of Earth’s core and present-day internal structure.
Fig. 2: Concentrations of elements in bulk silicate Earth relative to primitive meteorites.
Fig. 3: The effects of light elements and Ni on outer core density and velocity.
Fig. 4: Possible range of the inner core composition in the Fe–S–Si–C system.
Fig. 5: Constraints on liquid core composition.
Fig. 6: Implications of the core light elements.

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References

  1. Birch, F. Elasticity and constitution of the Earth’s interior. J. Geophys. Res. 57, 227–286 (1952).

    Article  Google Scholar 

  2. Birch, F. Density and composition of mantle and core. J. Geophys. Res. 69, 4377–4388 (1964).

    Article  Google Scholar 

  3. Nomura, R. et al. Low core-mantle boundary temperature inferred from the solidus of pyrolite. Science 343, 522–525 (2014).

    Article  Google Scholar 

  4. Kim, T. et al. Low melting temperature of anhydrous mantle materials at the core-mantle boundary. Geophys. Res. Lett. 47, e2020GL089345 (2020).

    Article  Google Scholar 

  5. Lay, T., Hernlund, J. & Buffett, B. A. Core–mantle boundary heat flow. Nat. Geosci. 1, 25–32 (2008).

    Article  Google Scholar 

  6. Fischer, R. A. in Deep Earth: Physics and Chemistry of the Lower Mantle and Core, Geophysical Monograph Series Vol. 217 (eds Terasaki, H. & Fischer, R. A.) 1–12 (American Geophysical Union, 2016).

  7. Dziewonski, A. M. & Anderson, D. L. Preliminary reference Earth model. Phys. Earth Planet. Inter. 25, 297–356 (1981).

    Article  Google Scholar 

  8. Raymond, S. N. & Morbidelli, A. Planet formation: key mechanisms and global models. Preprint at arXiv https://arxiv.org/pdf/2002.05756.pdf (2020).

  9. Thibault, Y. & Walter, M. J. The influence of pressure and temperature on the metal-silicate partition coefficients of nickel and cobalt in a model C1 chondrite and implications for metal segregation in a deep magma ocean. Geochim. Cosmochim. Acta 59, 991–1002 (1995). The first study to show that Ni and Co become less siderophile with increasing pressure and that segregation of core metal at the base of a deep magma ocean could explain the Ni and Co contents of the bulk silicate Earth.

    Article  Google Scholar 

  10. Li, J. & Agee, C. B. Geochemistry of mantle–core differentiation at high pressure. Nature 381, 686–689 (1996).

    Article  Google Scholar 

  11. Wood, B. J., Walter, M. J. & Wade, J. Accretion of the Earth and segregation of its core. Nature 441, 825–833 (2006).

    Article  Google Scholar 

  12. Poirier, J.-P. Light elements in the Earth’s outer core: a critical review. Phys. Earth Planet. Inter. 85, 319–337 (1994).

    Article  Google Scholar 

  13. Hirose, K., Labrosse, S. & Hernlund, J. Composition and state of the core. Annu. Rev. Earth Planet. Sci. 41, 657–691 (2013).

    Article  Google Scholar 

  14. Li, J. in Encyclopedia of Geology 2nd edn (eds Elias, S. & Alderton, D.) 150–163 (Elsevier, 2021).

  15. Speelmanns, I. M., Schmidt, M. W. & Liebske, C. The almost lithophile character of nitrogen during core formation. Earth Planet. Sci. Lett. 510, 186–197 (2019).

    Article  Google Scholar 

  16. Grewal, D. S., Dasgupta, R., Hough, T. & Farnell, A. Rates of protoplanetary accretion and differentiation set nitrogen budget of rocky planets. Nat. Geosci. 14, 369–376 (2021).

    Article  Google Scholar 

  17. Blanchard, I., Siebert, J., Borensztajn, S. & Badro, J. The solubility of heat-producing elements in Earth’s core. Geochem. Perspect. Lett. 5, 1–5 (2017).

    Google Scholar 

  18. Badro, J. et al. Magnesium partitioning between Earth’s mantle and core and its potential to drive an early exsolution geodynamo. Geophys. Res. Lett. 45, 13,240–13,248 (2018).

    Article  Google Scholar 

  19. Du, Z., Boujibar, A., Driscoll, P. & Fei, Y. Experimental constraints on an MgO exsolution-driven dynamo. Geophys. Res. Lett. 44, 7379–7385 (2019).

    Article  Google Scholar 

  20. Deguen, R., Olson, P. & Cardin, P. Experiments on turbulent metal-silicate mixing in a magma ocean. Earth Planet. Sci. Lett. 310, 303–313 (2011).

    Article  Google Scholar 

  21. Suer, T. A., Siebert, J., Remusat, L., Menguy, N. & Fiquet, G. A sulfur-poor terrestrial core inferred from metal–silicate partitioning experiments. Earth Planet. Sci. Lett. 469, 84–97 (2017).

    Article  Google Scholar 

  22. Fischer, R. et al. High pressure metal–silicate partitioning of Ni, Co, V, Cr, Si, and O. Geochim. Cosmochim. Acta 167, 177–194 (2015).

    Article  Google Scholar 

  23. Hirose, K. et al. Crystallization of silicon dioxide and compositional evolution of the Earth’s core. Nature 543, 99–102 (2017).

    Article  Google Scholar 

  24. Fischer, R., Cottrell, E., Hauri, E., Lee, K. K. M. & Le Voyer, M. The carbon content of Earth and its core. Proc. Natl Acad. Sci. USA 117, 8743–8749 (2020).

    Article  Google Scholar 

  25. Li, Y., Vočadlo, L., Sun, T. & Brodholt, J. P. The Earth’s core as a reservoir of water. Nat. Geosci. 13, 453–458 (2020). Ab initio calculations showing how water partitions between silicate and metal, thus, showing that the Earth’s core may act as a large reservoir for water.

    Article  Google Scholar 

  26. Yuan, L. & Steinle-Neumann, G. Strong sequestration of hydrogen into the Earth’s core during planetary differentiation. Geophys. Res. Lett. 47, e2020GL088303 (2020).

    Article  Google Scholar 

  27. Tagawa, S. et al. Experimental evidence for hydrogen incorporation into Earth’s core. Nat. Commun. 12, 2588 (2021). Experimentally determined the partitioning of hydrogen between liquid Fe and molten silicate under high pressure and high temperature corresponding to conditions of core-forming metal segregation from silicate.

    Article  Google Scholar 

  28. McDonough, W. F. in Treatise on Geochemistry 2nd edn Vol. 3 (eds Holland, H. D. & Turekian, K. K.) 559–576 (Elsevier, 2013).

  29. Badro, J., Côté, A. S. & Brodholt, J. P. A seismologically consistent compositional model of Earth’s core. Proc. Natl Acad. Sci. USA 111, 7542–7545 (2014).

    Article  Google Scholar 

  30. Umemoto, K. & Hirose, K. Chemical compositions of the outer core examined by first principles calculations. Earth Planet. Sci. Lett. 531, 116009 (2020). Theoretically calculated the possible range of outer core composition in the Fe–Ni–S–Si–O–C–H system that accounts for observed density and velocity.

    Article  Google Scholar 

  31. Irving, J. C. E., Cottaar, S. & Lekic, V. Seismically determined elastic parameters for Earth’s outer core. Sci. Adv. 4, eaar2538 (2018).

    Article  Google Scholar 

  32. Vočadlo, L., Gillan, M. J. & Price, G. D. The properties of iron under core conditions from first principles calculations. Phys. Earth Planet. Inter. 140, 101–125 (2003). Ab initio calculations giving a range of properties for solid and liquid iron at core conditions of pressure and temperature.

    Article  Google Scholar 

  33. Kuwayama, Y. et al. Equation of state of liquid iron under extreme conditions. Phys. Rev. Lett. 124, 165701 (2020). Experimentally determined the equation of state of liquid iron by a combination of X-ray diffraction and inelastic X-ray scattering measurements to high pressure and high temperature close to core conditions.

    Article  Google Scholar 

  34. Morard, G. et al. The Earth’s core composition from high pressure density measurements of liquid iron alloys. Earth Planet. Sci. Lett. 373, 169–178 (2013).

    Article  Google Scholar 

  35. Kawaguchi, S. et al. Sound velocity of liquid Fe–Ni–S at high pressure. J. Geophys. Res. Solid Earth 122, 3624–3634 (2017).

    Article  Google Scholar 

  36. Morard, G. et al. Structure and density of Fe-C liquid alloys under high pressure. J. Geophys. Res. Solid Earth 122, 7813–7823 (2017).

    Article  Google Scholar 

  37. Nakajima, Y. et al. Silicon-depleted present-day Earth’s outer core revealed by sound velocity measurements of liquid Fe-Si alloy. J. Geophys. Res. Solid Earth 125, e2020JB019399 (2020).

    Article  Google Scholar 

  38. Nakajima, Y. et al. Carbon-depleted outer core revealed by sound velocity measurements of liquid iron–carbon alloy. Nat. Commun. 6, 8942 (2015).

    Article  Google Scholar 

  39. Dewaele, A. et al. Quasihydrostatic equation of state of iron above 2 Mbar. Phys. Rev. Lett. 97, 215504 (2006).

    Article  Google Scholar 

  40. Fei, Y., Murphy, C., Shibazaki, Y., Shahar, A. & Huang, H. Thermal equation of state of hcp-iron: Constraint on the density deficit of Earth’s solid inner core. Geophys. Res. Lett. 43, 6837–6843 (2016).

    Article  Google Scholar 

  41. Mao, Z. et al. Sound velocities of Fe and Fe-Si alloy in the Earth’s core. Proc. Natl. Acad. Sci. USA 109, 10,239–10,244 (2012).

    Article  Google Scholar 

  42. Antonangeli, D. et al. Sound velocities and density measurements of solid hcp-Fe and hcp-Fe–Si (9 wt.%) alloy at high pressure: constraints on the Si abundance in the Earth’s inner core. Earth Planet. Sci. Lett. 482, 446–453 (2018).

    Article  Google Scholar 

  43. Li, Y., Vočadlo, L. & Brodholt, J. P. The elastic properties of hcp-Fe alloys under the conditions of the Earth’s inner core. Earth Planet. Sci. Lett. 493, 118–127 (2018). Ab initio determination of inner core compositions that match seismological observations.

    Article  Google Scholar 

  44. Wang, W. et al. Strong shear softening induced by superionic hydrogen in Earth’s inner core. Earth Planet. Sci. Lett. 568, 117014 (2021).

    Article  Google Scholar 

  45. Tateno, S. et al. Melting experiments on Fe-Si-S alloys to core pressures: Silicon in the core? Am. Mineral. 103, 742–748 (2018).

    Article  Google Scholar 

  46. Yokoo, S., Hirose, K., Sinmyo, R. & Tagawa, S. Melting experiments on liquidus phase relations in the Fe-S-O ternary system under core pressures. Geophys. Res. Lett. 46, 5137–5145 (2019). Determined the liquidus phase relations in the Fe–S–O ternary system, showing the possible compositional range of the outer core liquid that crystallizes Fe at the inner core.

    Article  Google Scholar 

  47. Hasegawa, M., Hirose, K., Oka, K. & Ohishi, Y. Liquidus phase relations and solid-liquid partitioning in the Fe-Si-C system under core pressures. Geophys. Res. Lett. 48, e2021GL092681 (2021).

    Article  Google Scholar 

  48. Tao, R. & Fei, Y. High-pressure experimental constraints of partitioning behavior of Si and S at the Mercury’s inner core boundary. Earth Planet. Sci. Lett. 562, 116849 (2021).

    Article  Google Scholar 

  49. Wood, B. J., Smythe, D. J. & Harrison, T. The condensation temperatures of the elements: A reappraisal. Am. Mineral. 104, 844–856 (2019). A review and revision of element condensation temperatures and volatilities in the solar nebula and their relationships to abundances in the bulk silicate Earth.

    Article  Google Scholar 

  50. Dreibus, G. & Palme, H. Cosmochemical constraints on the sulfur content in the Earth’s core. Geochim. Cosmochim. Acta 60, 1125–1130 (1996).

    Article  Google Scholar 

  51. Allègre, C. J., Poirier, J.-P., Humler, E. & Hofmann, A. W. The chemical composition of the Earth. Earth Planet. Sci. Lett. 134, 515–526 (1995).

    Article  Google Scholar 

  52. Georg, R. B., Halliday, A. N., Schauble, E. A. & Reynolds, B. C. Silicon in the Earth’s core. Nature 447, 1102–1106 (2007). Showed that the difference in silicon isotopic composition between the bulk silicate Earth and chondrites could be explained by partitioning of Si (~5 wt%) into Earth’s core.

    Article  Google Scholar 

  53. Shahar, A. et al. Experimentally determined Si isotope fractionation between silicate and Fe metal and implications for Earth’s core formation. Earth Planet. Sci. Lett. 288, 228–234 (2009).

    Article  Google Scholar 

  54. Hin, R. C., Fitoussi, C., Schmidt, M. W., & Bourdon, B. Experimental determination of the Si isotope fractionation factor between liquid metal and liquid silicate. Earth Planet. Sci. Lett. 387, 55–66 (2014).

    Article  Google Scholar 

  55. Dauphas, N., Poitrasson, F., Burkhardt, C., Kobayashi, H. & Kurosawa, K. Planetary and meteoritic Mg/Si and δ30Si variations inherited from solar nebula chemistry. Earth Planet. Sci. Lett. 427, 236–248 (2015).

    Article  Google Scholar 

  56. Wasson, J. T. & Kallemeyn, G. W. Compositions of chondrites. Philos. Trans. R. Soc. Lond. 325, 535–544 (1988).

    Article  Google Scholar 

  57. Alfè, D., Gillan, M. J. & Price, G. D. Composition and temperature of the Earth’s core constrained by combining ab initio calculations and seismic data. Earth Planet. Sci. Lett. 195, 91–98 (2002). Ab initio calculations showing that oxygen cannot go into the inner core, and sulfur and silicon equipartition between the inner and outer core, which has significant implications for the composition of the core as a whole.

    Article  Google Scholar 

  58. Anderson, W. W. & Ahrens, T. J. An equation of state for liquid iron and implications for the Earth’s core. J. Geophys. Res. Solid Earth 99, 4273–4284 (1994).

    Article  Google Scholar 

  59. Sata, N. et al. Compression of FeSi, Fe3C, Fe0.95O, and FeS under the core pressures and implication for light element in the Earth’s core. J. Geophys. Res. Solid Earth 115, B09204 (2010).

    Article  Google Scholar 

  60. Terasaki, H. et al. Stability of Fe–Ni hydride after the reaction between Fe–Ni alloy and hydrous phase (δ-AlOOH) up to 1.2 Mbar: Possibility of H contribution to the core density deficit. Phys. Earth Planet. Inter. 194–195, 18–24 (2012).

    Article  Google Scholar 

  61. Jing, Z. et al. Sound velocity of Fe–S liquids at high pressure: Implications for the Moon’s molten outer core. Earth Planet. Sci. Lett. 396, 78–87 (2014).

    Article  Google Scholar 

  62. Nishida, K. et al. Effect of sulfur on sound velocity of liquid iron under Martian core conditions. Nat. Commun. 11, 1954 (2020).

    Article  Google Scholar 

  63. Ozawa, H., Hirose, K., Tateno, S., Sata, N. & Ohishi, Y. Phase transition boundary between B1 and B8 structures of FeO up to 210 GPa. Phys. Earth Planet. Inter. 179, 157–163 (2010).

    Article  Google Scholar 

  64. Chen, B. et al. Hidden carbon in Earth’s inner core revealed by shear softening in dense Fe7C3. Proc. Natl Acad. Sci. USA 111, 17755–17758 (2014).

    Article  Google Scholar 

  65. Prescher, C. et al. High Poisson’s ratio of Earth’s inner core explained by carbon alloying. Nat. Geosci. 8, 220–223 (2015).

    Article  Google Scholar 

  66. Sakamaki, T. et al. Constraints on Earth’s inner core composition inferred from measurements of the sound velocity of hcp-iron in extreme conditions. Sci. Adv. 2, e1500802 (2016).

    Article  Google Scholar 

  67. Masters, G. & Gubbins, D. On the resolution of density within the Earth. Phys. Earth Planet. Inter. 140, 159–167 (2003).

    Article  Google Scholar 

  68. Vočadlo, L. et al. The stability of bcc-Fe at high pressures and temperatures with respect to tetragonal strain. Phys. Earth Planet. Int. 170, 52–59 (2008).

    Article  Google Scholar 

  69. Tateno, S., Hirose, K., Ohishi, Y. & Tatsumi, Y. The structure of iron in Earth’s inner core. Science 330, 359–361 (2010).

    Article  Google Scholar 

  70. Jackson, I., Fitz Gerald, J. D. & Kokkonen, H. High temperature viscoelastic relaxation in iron and its implications for the shear modulus and attenuation of the Earth’s inner core. J. Geophys. Res. Solid Earth 105, 23605–23634 (2000).

    Article  Google Scholar 

  71. Li, Y., Vočadlo, L., Brodholt, J. & Wood, I. G. Thermoelasticity of Fe7C3 under inner core conditions. J. Geophys. Res. Solid Earth 121, 5828–5837 (2016).

    Article  Google Scholar 

  72. Tateno, S. et al. Fe2S: the most Fe-rich iron sulfide at the Earth’s inner core pressures. Geophys. Res. Lett. 46, 11944–11949 (2019).

    Article  Google Scholar 

  73. Mashino, I. et al. Melting experiments on the Fe–C binary system up to 255 GPa: Constraints on the carbon content in the Earth’s core. Earth Planet. Sci. Lett. 515, 135–144 (2019).

    Article  Google Scholar 

  74. Fukai, Y. in High-Pressure Research: Application to Earth and Planetary Sciences, Geophysical Monograph Series Vol. 67 (eds Syono, Y. & Manghnani, M. H.) 373–385 (Terra Scientific Publishing Company (TERRAPUB), 1992).

  75. Mori, Y. et al. Melting experiments on Fe–Fe3S system to 254 GPa. Earth Planet. Sci. Lett. 464, 135–141 (2017).

    Article  Google Scholar 

  76. Oka, K. et al. Melting in the Fe-FeO system to 204 GPa: Implications for oxygen in Earth’s core. Am. Mineral. 104, 1603–1607 (2019).

    Article  Google Scholar 

  77. Stewart, A. J., Schmidt, M. W., van Westrenen, W. & Liebske, C. Mars: A new core-crystallization regime. Science 316, 1323–1325 (2007).

    Article  Google Scholar 

  78. Gilfoy, F. & Li, J. Thermal state and solidification regime of the martian core: Insights from the melting behavior of FeNi-S at 20 GPa. Earth Planet. Sci. Lett. 541, 116285 (2020).

    Article  Google Scholar 

  79. Imai, T. Crystal/melt partitioning under deep mantle conditions and melting phase relation in the system Fe-FeH. Doctoral thesis, Tokyo Inst. Technol. (2013).

  80. Pépin, C. M., Dewaele, A., Geneste, G. & Loubeyre, P. New iron hydrides under high pressure. Phys. Rev. Lett. 113, 265504 (2014).

    Article  Google Scholar 

  81. O’Neill, H. S. C., Canil, D. & Rubie, D. C. Oxide-metal equilibria to 2500°C and 25 GPa: implications for core formation and the light component in the Earth’s core. J. Geophys. Res. Solid Earth 103, 12239–12260 (1998).

    Article  Google Scholar 

  82. Takahashi, S. et al. Phase relations in the carbon-saturated C–Mg–Fe–Si–O system and C and Si solubility in liquid Fe at high pressure and temperature: implications for planetary interiors. Phys. Chem. Miner. 40, 647–657 (2013).

    Article  Google Scholar 

  83. Hirose, K. et al. Hydrogen limits carbon in liquid iron. Geophys. Res. Lett. 46, 5190–5197 (2019).

    Article  Google Scholar 

  84. Helffrich, G., Hirose, K. & Nomura, R. Thermodynamical modeling of liquid Fe-Si-Mg-O: molten magnesium silicate release from the core. Geophys. Res. Lett. 47, e2020GL089218 (2020).

    Article  Google Scholar 

  85. Mittal, T. et al. Precipitation of multiple light elements to power Earth’s early dynamo. Earth Planet. Sci. Lett. 532, 116030 (2020).

    Article  Google Scholar 

  86. Arveson, S. M., Deng, J., Karki, B. B. & Lee, K. K. M. Evidence for Fe-Si-O liquid immiscibility at deep Earth pressures. Proc. Natl Acad. Sci. USA 116, 10,238–10,243 (2019).

    Article  Google Scholar 

  87. Ringwood, A. E. in Advances in Earth Science (ed. Hurley, P. M.) 287–356 (MIT Press, 1966).

  88. Palme, H. & O’Neill, H. St. C. in Treatise on Geochemistry 2nd edn Vol. 3 (eds Holland, H. D. & Turekian, K. K.) 1–39 (Elsevier, 2014).

  89. Wade, J. & Wood, B. J. Core formation and the oxidation state of the Earth. Earth Planet. Sci. Lett. 236, 78–95 (2005). Used experimental metal–silicate partitioning data to show that a continuous accretion model in which the Earth grew from a small, reduced body to a large, more oxidized body could explain the current composition of the bulk silicate Earth.

    Article  Google Scholar 

  90. Wade, J., Wood, B. J. & Tuff, J. Metal–silicate partitioning of Mo and W at high pressures and temperatures: evidence for late accretion of sulphur to the Earth. Geochim. Cosmochim. Acta 85, 58–74 (2012).

    Article  Google Scholar 

  91. Wood, B. J. Accretion and core formation: constraints from metal–silicate partitioning. Philos. Trans. R. Soc. A 366, 4339–4355 (2008).

    Article  Google Scholar 

  92. Rubie, D. C. et al. Accretion and differentiation of the terrestrial planets with implications for the compositions of early-formed solar system bodies and accretion of water. Icarus 248, 89–108 (2015).

    Article  Google Scholar 

  93. Tuff, J., Wood, B. J. & Wade, J. The effect of Si on metal–silicate partitioning of siderophile elements and implications for the conditions of core formation. Geochim. Cosmochim. Acta 75, 673–690 (2011).

    Article  Google Scholar 

  94. Siebert, J., Badro, J., Antonangeli, D. & Ryerson, F. J. Terrestrial accretion under oxidising conditions. Science 339, 1194–1197 (2013).

    Article  Google Scholar 

  95. Wood, B. J. Carbon in the core. Earth Planet. Sci. Lett. 117, 593–607 (1993).

    Article  Google Scholar 

  96. Iizuka-Oku, R. et al. Hydrogenation of iron in the early stage of Earth’s evolution. Nat. Commun. 8, 14096 (2017).

    Article  Google Scholar 

  97. Clesi, V. et al. Low hydrogen contents in the cores of terrestrial planets. Sci. Adv. 4, e1701876 (2018).

    Article  Google Scholar 

  98. Malavergne, V. et al. Experimental constraints on the fate of H and C during planetary core-mantle differentiation. Implications for the Earth. Icarus 321, 473–485 (2019).

    Article  Google Scholar 

  99. Satish-Kumar, M., So, H., Yoshino, T., Kato, M. & Hiroi, Y. Experimental determination of carbon isotope fractionation between iron carbide melt and carbon: 12C-enriched carbon in the Earth’s core? Earth Planet. Sci. Lett. 310, 340–348 (2011).

    Article  Google Scholar 

  100. Labidi, J. et al. Experimentally determined sulfur isotope fractionation between metal and silicate and implications for planetary differentiation. Geochim. Cosmochim. Acta 175, 181–194 (2016).

    Article  Google Scholar 

  101. Allègre, C., Manhès, G. & Lewin, È. Chemical composition of the Earth and the volatility control on planetary genetics. Earth Planet. Sci. Lett. 185, 49–69 (2001).

    Article  Google Scholar 

  102. Morard, G. et al. Fe–FeO and Fe–Fe3C melting relations at Earth’s core–mantle boundary conditions: Implications for a volatile-rich or oxygen-rich core. Earth Planet. Sci. Lett. 473, 94–103 (2017).

    Article  Google Scholar 

  103. Alfè, D. Temperature of the inner-core boundary of the Earth: Melting of iron at high pressure from first-principles coexistence simulations. Phys. Rev. B 79, 060101(R) (2009).

    Article  Google Scholar 

  104. Hernlund, J. W. & McNamara, A. K. in Treatise on Geophysics 2nd edn Vol. 7 (ed. Schubert, G.) 461–519 (Elsevier, 2015).

  105. Hirose, K., Wentzcovitch, R., Yuen, D. & Lay, T. in Treatise on Geophysics 2nd edn Vol. 2 (ed. Schubert, G.) 85–115 (Elsevier, 2015).

  106. Koppers, A. A. P. et al. Mantle plumes and their role in Earth processes. Nat. Rev. Earth Environ. 2, 382–401 (2021).

    Article  Google Scholar 

  107. Williams, Q. & Garnero, E. J. Seismic evidence for partial melt at the base of Earth’s mantle. Science 273, 1528–1530 (1996).

    Article  Google Scholar 

  108. Wicks, J. K., Jackson, J. M. & Sturhahn, W. Very low sound velocities in iron-rich (Mg,Fe)O: Implications for the core-mantle boundary region. Geophys. Res. Lett. 37, L15304 (2010).

    Article  Google Scholar 

  109. Cobden, L., Mosca, I., Trampert, J. & Ritsema, J. On the likelihood of post-perovskite near the core–mantle boundary: A statistical interpretation of seismic observations. Phys. Earth Planet. Inter. 210–211, 21–35 (2012).

    Article  Google Scholar 

  110. Souriau, A. & Calvet, M. in Treatise on Geophysics 2nd edn Vol. 1 (ed. Schubert, G.) 725–757 (Elsevier, 2015).

  111. Vočadlo, L. in Encyclopedia of Geomagnetism and Paleomagnetism (eds Gubbins, D. & Herrero-Bervera, E.) 104 (Springer, 2007).

  112. Lasbleis, M. & Deguen, R. Building a regime diagram for the Earth’s inner core. Phys. Earth Planet. Inter. 247, 80–93 (2015).

    Article  Google Scholar 

  113. Belonoshko, A. B., Fu, J., Bryk, T., Simak, S. I. & Mattesini, M. Low viscosity of the Earth’s inner core. Nat. Commun. 10, 2483 (2019).

    Article  Google Scholar 

  114. Reaman, D. M., Daehn, G. S. & Panero, W. R. Predictive mechanism for anisotropy development in the Earth’s inner core. Earth Planet. Sci. Lett. 312, 437–442 (2011).

    Article  Google Scholar 

  115. Hirschmann, M. M. Constraints on the early delivery and fractionation of Earth’s major volatiles from C/H, C/N, and C/S ratios. Am. Mineral. 101, 540–553 (2016).

    Article  Google Scholar 

  116. Tateno, S., Hirose, K. & Ohishi, Y. Melting experiments on peridotite to lowermost mantle conditions. J. Geophys. Res. Solid Earth 119, 4684–4694 (2014).

    Article  Google Scholar 

  117. Caracas, R., Hirose, K., Nomura & Ballmer, M. D. Melt–crystal density crossover in a deep magma ocean. Earth Planet. Sci. Lett. 516, 202–211 (2019).

    Article  Google Scholar 

  118. Ballmer, M., Houser, C., Hernlund, J., Wentzcovitch, R. & Hirose, K. Persistence of strong silica-enriched domains in the Earth’s lower mantle. Nat. Geosci. 10, 236–240 (2017).

    Article  Google Scholar 

  119. Badro, J., Brodholt, J. P., Piet, H., Siebert, J. & Ryerson, F. J. Core formation and core composition from coupled geochemical and geophysical constraints. Proc. Natl Acad. Sci. USA 112, 12310–12314 (2015).

    Article  Google Scholar 

  120. Walsh, K. J., Morbidelli, A., Raymond, S. N., O’Brien, D. P. & Mandell, A. M. A low mass for Mars from Jupiter’s early gas-driven migration. Nature 475, 206–209 (2011).

    Article  Google Scholar 

  121. Sato, T., Okuzumi, S. & Ida, S. On the water delivery to terrestrial embryos by ice pebble accretion. Astron. Astrophys. 589, A15 (2016).

    Article  Google Scholar 

  122. Raymond, S. N., Quinn, T. & Lunine, J. I. High-resolution simulations of the final assembly of Earth-like planets. 2. Water delivery and planetary habitability. Astrobiology 7, 66–84 (2007).

    Article  Google Scholar 

  123. Hirschmann, M. M. & Dasgupta, R. The H/C ratios of Earth’s near-surface and deep reservoirs, and consequences for deep Earth volatile cycles. Chem. Geol. 262, 4–16 (2009).

    Article  Google Scholar 

  124. Wei, C.-E. et al. The effect of carbon grain destruction on the chemical structure of protoplanetary disks. Astrophys. J. 870, 129 (2019).

    Article  Google Scholar 

  125. Ikoma, M. & Genda, H. Constraints on the mass of a habitable planet with water of nebular origin. Astrophys. J. 648, 696–706 (2006).

    Article  Google Scholar 

  126. Olson, P. & Sharp, Z. D. Nebular atmosphere to magma ocean: a model for volatile capture during Earth accretion. Phys. Earth Planet. Inter. 294, 106294 (2019).

    Article  Google Scholar 

  127. Hallis, L. J. et al. Evidence for primordial water in Earth’s deep mantle. Science 350, 336–339 (2015).

    Article  Google Scholar 

  128. Gomi, H. et al. The high conductivity of iron and thermal evolution of the Earth’s core. Phys. Earth Planet. Inter. 224, 88–103 (2013).

    Article  Google Scholar 

  129. Ohta, K., Suehiro, S., Hirose, K. & Ohishi, Y. Electrical resistivity of fcc phase iron hydrides at high pressures and temperatures. C. R. Geosci. 351, 147–153 (2019).

    Article  Google Scholar 

  130. Gomi, H., Hirose, K., Akai, H. & Fei, Y. Electrical resistivity of substitutionally disordered hcp Fe–Si and Fe–Ni alloys: Chemically-induced resistivity saturation in the Earth’s core. Earth Planet. Sci. Lett. 451, 51–61 (2016).

    Article  Google Scholar 

  131. Inoue, H., Suehiro, S., Ohta, K., Hirose, K. & Ohishi, Y. Resistivity saturation of hcp Fe-Si alloys in an internally heated diamond anvil cell: A key to assessing the Earth’s core conductivity. Earth Planet. Sci. Lett. 543, 116357 (2020).

    Article  Google Scholar 

  132. Zhang, Y. et al. Reconciliation of experiments and theory on transport properties of iron and the geodynamo. Phys. Rev. Lett. 125, 078501 (2020).

    Article  Google Scholar 

  133. Ohta, K. & Hirose, K. The thermal conductivity of the Earth’s core and implications for its thermal and compositional evolution. Nat. Sci. Rev. 8, nwaa303 (2021).

    Article  Google Scholar 

  134. Labrosse, S. Thermal evolution of the core with a high thermal conductivity. Phys. Earth Planet. Inter. 247, 36–55 (2015).

    Article  Google Scholar 

  135. Tarduno, J. A. et al. Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo. Proc. Natl Acad. Sci. USA 117, 2309–2318 (2020).

    Article  Google Scholar 

  136. Pozzo, M., Davies, C., Gubbins, D. & Alfè, D. Thermal and electrical conductivity of iron at Earth’s core conditions. Nature 485, 355–358 (2012).

    Article  Google Scholar 

  137. Olson, P. The new core paradox. Science 342, 431–432 (2015).

    Article  Google Scholar 

  138. O’Rourke, J. G. & Stevenson, D. J. Powering Earth’s dynamo with magnesium precipitation from the core. Nature 529, 387–389 (2016).

    Article  Google Scholar 

  139. Badro, J., Siebert, J. & Nimmo, F. An early geodynamo driven by exsolution of mantle components from Earth’s core. Nature 536, 326–328 (2016).

    Article  Google Scholar 

  140. Du, Z. et al. Insufficient energy from MgO exsolution to power early geodynamo. Geophys. Res. Lett. 44, 11,376–11,381 (2017).

    Article  Google Scholar 

  141. Boehler, R. Temperatures in the Earth’s core from melting-point measurements of iron at high static pressures. Nature 363, 534–536 (1993).

    Article  Google Scholar 

  142. Anzellini, S., Dewaele, A., Mezouar, M., Loubeyre, P. & Morard, G. Melting of iron at Earth’s inner core boundary based on fast X-ray diffraction. Science 340, 464–466 (2013).

    Article  Google Scholar 

  143. Sinmyo, R., Hirose, K. & Ohishi, Y. Melting curve of iron to 290 GPa determined in a resistance-heated diamond-anvil cell. Earth Planet. Sci. Lett. 510, 45–52 (2019).

    Article  Google Scholar 

  144. Helffrich, G. & Kaneshima, S. Outer-core compositional stratification from observed core wave speed profiles. Nature 468, 807–812 (2010).

    Article  Google Scholar 

  145. Brodholt, J. & Badro, J. Composition of the low seismic velocity E′ layer at the top of Earth’s core. Geophys. Res. Lett. 44, 8303–8310 (2017).

    Article  Google Scholar 

  146. Labrosse, S., Hernlund, J. W. & Coltice, N. A crystallizing dense magma ocean at the base of the Earth’s mantle. Nature 450, 866–869 (2007).

    Article  Google Scholar 

  147. Helffrich, G. Outer core compositional layering and constraints on core liquid transport properties. Earth Planet. Sci. Lett. 391, 256–262 (2014).

    Article  Google Scholar 

  148. Biggin, A. et al. Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation. Nature 526, 245–248 (2015).

    Article  Google Scholar 

  149. 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).

    Article  Google Scholar 

  150. Ozawa, H., Hirose, K., Yonemitsu, K. & Ohishi, Y. High-pressure melting experiments on Fe–Si alloys and implications for silicon as a light element in the core. Earth Planet. Sci. Lett. 456, 47–54 (2016).

    Article  Google Scholar 

  151. Li, Y., Vočadlo, L., Alfè, D. & Brodholt, J. P. Carbon partitioning between the Earth’s inner and outer core. J. Geophys. Res. Solid Earth 124, 12812–12824 (2019).

    Article  Google Scholar 

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Acknowledgements

The authors thank K. Umemoto for his help in preparing the manuscript.

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Authors and Affiliations

  1. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan

    Kei Hirose

  2. Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan

    Kei Hirose

  3. Department of Earth Sciences, University of Oxford, Oxford, UK

    Bernard Wood

  4. Department of Earth Sciences, University College London, London, UK

    Lidunka Vočadlo

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  1. Kei Hirose
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  2. Bernard Wood
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Glossary

Bulk silicate Earth

(BSE). Refers to the chemical composition of silicate Earth, after accretion and core segregation, but before differentiation of the first crust.

Ab initio calculations

Purely theoretical calculations without inputs from experimental results.

Static compression experiments

Experiments in which a given high-pressure (and high-temperature) condition is kept for a certain period of time. It is the opposite of ‘dynamic compression experiments’, in which high-pressure and high-temperature conditions are generated in a very short period of time (~1 µs).

Carbonaceous chondrite meteorites

A group of C-rich primitive meteorites.

CI chondrites

Primitive meteorites with compositions similar to that of the Solar System for refractory elements.

Refractory

Materials like metals and silicates that have a high equilibrium condensation temperature (the opposite of volatile).

Chondritic reference

Reference based on primitive meteorites that are similar in composition to the Solar System.

Diamond anvil cell

(DAC). A device generating high pressure within a specimen by compressing it between a set of diamonds (the hardest material known to date).

hcp Structure

Hexagonal close-packed crystal structure, one of the closest packed structures.

Eutectic point

A composition and a temperature at which eutectic melting (melting in a two-or-more-component system in which all components are not soluble into a single solid phase) occurs.

Eutectic liquids

Liquids coexisting with the number of solid phases in a two-or-more-component system in which all components are not soluble into a single solid phase.

Simultaneous solubility limits

The maximum amounts of two (or more) elements that dissolve together into a liquid.

bcc Fe

Solid iron with the body-centred cubic crystal structure.

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Hirose, K., Wood, B. & Vočadlo, L. Light elements in the Earth’s core. Nat Rev Earth Environ 2, 645–658 (2021). https://doi.org/10.1038/s43017-021-00203-6

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