Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The Earth’s core as a reservoir of water

Abstract

Current estimates of the budget and distribution of water in the Earth have large uncertainties, most of which are due to the lack of information about the deep Earth. Recent studies suggest that the Earth could have gained a considerable amount of water during the early stages of its evolution from the hydrogen-rich solar nebula, and that a large amount of the water in the Earth may have partitioned into the core. Here we calculate the partitioning of water between iron and silicate melts at 20–135 GPa and 2,800–5,000 K, using ab initio molecular dynamics and thermodynamic integration techniques. Our results indicate a siderophile nature of water at core–mantle differentiation and core–mantle boundary conditions, which weakens with increasing temperature; nevertheless, we found that water always partitions strongly into the iron liquid under core-formation conditions for both reducing and oxidizing scenarios. The siderophile nature of water was also verified by an empirical-counting method that calculates the distribution of hydrogen in an equilibrated iron and silicate melt. We therefore conclude that the Earth’s core may act as a large reservoir that contains most of the Earth’s water. In addition to constraining the accretion models of volatile delivery, the findings may partially account for the low density of the Earth’s core implied by measured seismic velocities.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Calculated free energies.
Fig. 2: Partition coefficient.
Fig. 3: Temperature dependence of H partitioning.
Fig. 4: Empirical counting of H partitioning.
Fig. 5: Comparison of partition coefficients with the literature.

Data availability

The raw outputs can be accessed in the UK National Geoscience Data Centre (NGDC) (https://doi.org/10.5285/d0677edf-c987-497d-aae8-23bf22ef774d). Any additional data can be requested by e-mailing the corresponding author.

Code availability

The Vienna Ab Initio Simulation Package is a proprietary software available for purchase at https://www.vasp.at/.

References

  1. 1.

    Kuramoto, K. & Matsui, T. Partitioning of H and C between the mantle and core during the core formation in the Earth: its implications for the atmospheric evolution and redox state of early mantle. J. Geophys. Res. Planets 101, 14909–14932 (1996).

    Article  Google Scholar 

  2. 2.

    Okuchi, T. Hydrogen partitioning into molten iron at high pressure: implications for Earth’s core. Science 278, 1781–1784 (1997).

    Article  Google Scholar 

  3. 3.

    Shibazaki, Y., Ohtani, E., Terasaki, H., Suzuki, A. & Funakoshi, K. Hydrogen partitioning between iron and ringwoodite: implications for water transport into the Martian core. Earth Planet. Sci. Lett. 287, 463–470 (2009).

    Article  Google Scholar 

  4. 4.

    Zhang, Y. & Yin, Q.-Z. Carbon and other light element contents in the Earth’s core based on first-principles molecular dynamics. Proc. Natl Acad. Sci. USA 109, 19579–19583 (2012).

    Article  Google Scholar 

  5. 5.

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

    Article  Google Scholar 

  6. 6.

    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 

  7. 7.

    Alfè, D., de Wijs, G. A., Kresse, G. & Gillan, M. J. Recent developments in ab initio thermodynamics. Int. J. Quantum Chem. 77, 871–879 (2000).

    Article  Google Scholar 

  8. 8.

    Stixrude, L. & Karki, B. Structure and freezing of MgSiO3; liquid in Earth’s lower mantle. Science 310, 297–299 (2005).

    Article  Google Scholar 

  9. 9.

    Garnero, E. J., McNamara, A. K. & Shim, S.-H. Continent-sized anomalous zones with low seismic velocity at the base of Earth’s mantle. Nat. Geosci. 9, 481–489 (2016).

    Article  Google Scholar 

  10. 10.

    Pozzo, M., Davies, C., Gubbins, D. & Alfè, D. FeO content of Earth’s liquid core. Phys. Rev. 9, 041018 (2019).

    Article  Google Scholar 

  11. 11.

    Kaminsky, F. V. et al. Oxidation potential in the Earth’s lower mantle as recorded by ferropericlase inclusions in diamond. Earth Planet. Sci. Lett. 417, 49–56 (2015).

    Article  Google Scholar 

  12. 12.

    Fukai, Y., Mori, K. & Shinomiya, H. The phase diagram and superabundant vacancy formation in Fe–H alloys under high hydrogen pressures. J. Alloys Compd 348, 105–109 (2003).

    Article  Google Scholar 

  13. 13.

    Fukai, Y. The iron–water reaction and the evolution of the Earth. Nature 308, 174–175 (1984).

    Article  Google Scholar 

  14. 14.

    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 

  15. 15.

    Hu, Q. et al. FeO2 and FeOOH under deep lower-mantle conditions and Earth’s oxygen–hydrogen cycles. Nature 534, 241–244 (2016).

    Article  Google Scholar 

  16. 16.

    Wu, J. et al. Origin of Earth’s water: chondritic inheritance plus nebular ingassing and storage of hydrogen in the core. J. Geophys. Res. Planets 123, 2691–2712 (2018).

    Article  Google Scholar 

  17. 17.

    Bouhifd, M. A., Jephcoat, A. P., Heber, V. S. & Kelley, S. P. Helium in Earth’s early core. Nat. Geosci. 6, 982–986 (2013).

    Article  Google Scholar 

  18. 18.

    Mukhopadhyay, S. & Parai, R. Noble gases: a record of Earth’s evolution and mantle dynamics. Annu. Rev. Earth Planet. Sci. 47, 389–419 (2019).

    Article  Google Scholar 

  19. 19.

    Williams, C. D. & Mukhopadhyay, S. Capture of nebular gases during Earth’s accretion is preserved in deep-mantle neon. Nature 565, 78–81 (2019).

    Article  Google Scholar 

  20. 20.

    Olson, P. & Sharp, Z. D. Hydrogen and helium ingassing during terrestrial planet accretion. Earth Planet. Sci. Lett. 498, 418–426 (2018).

    Article  Google Scholar 

  21. 21.

    Tkalčić, H. & Pham, T. S. Shear properties of Earth’s inner core constrained by a detection of J waves in global correlation wavefield. Science 362, 329–332 (2018).

    Article  Google Scholar 

  22. 22.

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

    Article  Google Scholar 

  23. 23.

    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 

  24. 24.

    Umemoto, K. & Hirose, K. Liquid iron-hydrogen alloys at outer core conditions by first-principles calculations. Geophys. Res. Lett. 42, 7513–7520 (2015).

    Article  Google Scholar 

  25. 25.

    Nakagawa, T. & Iwamori, H. On the implications of the coupled evolution of the deep planetary interior and the presence of surface ocean water in hydrous mantle convection. C.R. Geosci. 351, 197–208 (2019).

    Article  Google Scholar 

  26. 26.

    Hernández, E. R., Alfè, D. & Brodholt, J. The incorporation of water into lower-mantle perovskites: a first-principles study. Earth Planet. Sci. Lett. 364, 37–43 (2013).

    Article  Google Scholar 

  27. 27.

    Militzer, B., Tagawa, S., Hirose, K. & Wahl, S. M. Ab initio simulations of hydrogen in the inner and outer core of the Earth. In AGU Fall Meeting 2016 Abstr. MR22A-03 (AGU, 2016).

  28. 28.

    Li, Y., Vočadlo, L. & Brodholt, J. The elastic properties of hcp-Fe alloys under the conditions of the Earth’s inner core. Earth Planet. Sci. Lett. 493, 118–127 (2018).

    Article  Google Scholar 

  29. 29.

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

    Article  Google Scholar 

  30. 30.

    Kresse, G. & Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6, 15–50 (1996).

    Article  Google Scholar 

  31. 31.

    Kresse, G. & Hafner, J. Ab initio molecular dynamics for open-shell transition metals. Phys. Rev. B 48, 13115–13118 (1993).

    Article  Google Scholar 

  32. 32.

    Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).

    Article  Google Scholar 

  33. 33.

    Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

    Article  Google Scholar 

  34. 34.

    Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

    Article  Google Scholar 

  35. 35.

    Edgington, A. L. The Structure, Composition and Evolution of Mercury’s Core PhD thesis, Univ. College London (2016).

  36. 36.

    Prescher, C. et al. Structurally hidden magnetic transitions in Fe3C at high pressures. Phys. Rev. B 85, 140402 (2012).

    Article  Google Scholar 

  37. 37.

    Sun, T., Brodholt, J. P., Li, Y. & Vočadlo, L. Melting properties from ab initio free energy calculations: iron at the Earth’s inner-core boundary. Phys. Rev. B 98, 224301 (2018).

    Article  Google Scholar 

  38. 38.

    Vočadlo, L. & Alfè, D. Ab initio melting curve of the fcc phase of aluminum. Phys. Rev. B 65, 214105 (2002).

    Article  Google Scholar 

  39. 39.

    Bharadwaj, A. S. & Singh, Y. Fluid–solid transition in simple systems using density functional theory. J. Chem. Phys. 143, 124503 (2015).

    Article  Google Scholar 

  40. 40.

    Mirzaeinia, A., Feyzi, F. & Hashemianzadeh, S. M. Equation of state and Helmholtz free energy for the atomic system of the repulsive Lennard-Jones particle. J. Chem. Phys. 147, 214503 (2017).

    Article  Google Scholar 

Download references

Acknowledgements

This work was supported by NERC grant NE/M015181/1 and NE/S01134X/1. We acknowledge the use of the NEXCS system, a collaborative facility supplied under the Joint Weather and Climate Research Program, a strategic partnership between the Met Office and the Natural Environment Research Council. This work also used the ARCHER UK National Supercomputing Service. T.S. acknowledges the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant no. XDB18000000).

Author information

Affiliations

Authors

Contributions

Y.L. carried out the simulations and analysis. L.V. and J.P.B. supervised the project. All the authors contributed to the data analysis and writing the paper.

Corresponding author

Correspondence to Yunguo Li.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Primary Handling Editor: Tamara Goldin.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Calculated free energies.

Calculated volumes and Gibbs free energies \(\bar G\left( {p,T,x} \right)\) of iron and silicate melts with H and H2O at 20, 50, 90, and 135 GPa, corresponding to temperatures of 2800, 3500, 3900 and 4200 K, respectively.

Extended Data Fig. 2 Temperature dependence of free energies.

Calculated volumes, enthalpies and Gibbs free energies \(\bar G\left( {p,T,x} \right)\) of Fe64, Fe64H4, (MgSiO3)32 and (MgSiO3)32H8 at temperatures from 4200 to 5000 K under 135 GPa.

Supplementary information

Supplementary Information

Supplementary Figs. 1–5, and discussion.

Supplementary Video 1

Two-phase AIMD Trajectory Video. The video shows that most hydrogen atoms (white balls) enter the liquid Fe (golden balls), but few go into the silicate melt (green, cyan and red balls represent Si, Mg and O, respectively) at ~50 GPa and 3,500 K. This simulation clearly demonstrates the siderophile (‘iron-loving’) nature of hydrogen, and implies that the Earth’s core can be a reservoir of hydrogen.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Li, Y., Vočadlo, L., Sun, T. et al. The Earth’s core as a reservoir of water. Nat. Geosci. 13, 453–458 (2020). https://doi.org/10.1038/s41561-020-0578-1

Download citation

Further reading

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing