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.
This is a preview of subscription content, access via your institution
Access options
Access Nature and 54 other Nature Portfolio journals
Get Nature+, our best-value online-access subscription
$29.99 / 30 days
cancel any time
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
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
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).
Okuchi, T. Hydrogen partitioning into molten iron at high pressure: implications for Earth’s core. Science 278, 1781–1784 (1997).
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).
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).
Clesi, V. et al. Low hydrogen contents in the cores of terrestrial planets. Sci. Adv. 4, e1701876 (2018).
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).
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).
Stixrude, L. & Karki, B. Structure and freezing of MgSiO3; liquid in Earth’s lower mantle. Science 310, 297–299 (2005).
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).
Pozzo, M., Davies, C., Gubbins, D. & Alfè, D. FeO content of Earth’s liquid core. Phys. Rev. 9, 041018 (2019).
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).
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).
Fukai, Y. The iron–water reaction and the evolution of the Earth. Nature 308, 174–175 (1984).
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).
Hu, Q. et al. FeO2 and FeOOH under deep lower-mantle conditions and Earth’s oxygen–hydrogen cycles. Nature 534, 241–244 (2016).
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).
Bouhifd, M. A., Jephcoat, A. P., Heber, V. S. & Kelley, S. P. Helium in Earth’s early core. Nat. Geosci. 6, 982–986 (2013).
Mukhopadhyay, S. & Parai, R. Noble gases: a record of Earth’s evolution and mantle dynamics. Annu. Rev. Earth Planet. Sci. 47, 389–419 (2019).
Williams, C. D. & Mukhopadhyay, S. Capture of nebular gases during Earth’s accretion is preserved in deep-mantle neon. Nature 565, 78–81 (2019).
Olson, P. & Sharp, Z. D. Hydrogen and helium ingassing during terrestrial planet accretion. Earth Planet. Sci. Lett. 498, 418–426 (2018).
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).
Hirose, K. et al. Crystallization of silicon dioxide and compositional evolution of the Earth’s core. Nature 543, 99–102 (2017).
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).
Umemoto, K. & Hirose, K. Liquid iron-hydrogen alloys at outer core conditions by first-principles calculations. Geophys. Res. Lett. 42, 7513–7520 (2015).
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).
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).
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).
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).
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).
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).
Kresse, G. & Hafner, J. Ab initio molecular dynamics for open-shell transition metals. Phys. Rev. B 48, 13115–13118 (1993).
Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).
Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).
Edgington, A. L. The Structure, Composition and Evolution of Mercury’s Core PhD thesis, Univ. College London (2016).
Prescher, C. et al. Structurally hidden magnetic transitions in Fe3C at high pressures. Phys. Rev. B 85, 140402 (2012).
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).
Vočadlo, L. & Alfè, D. Ab initio melting curve of the fcc phase of aluminum. Phys. Rev. B 65, 214105 (2002).
Bharadwaj, A. S. & Singh, Y. Fluid–solid transition in simple systems using density functional theory. J. Chem. Phys. 143, 124503 (2015).
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).
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
Authors and Affiliations
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
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
About this article
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
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41561-020-0578-1
This article is cited by
-
Earth shaped by primordial H2 atmospheres
Nature (2023)
-
Evidence for a liquid silicate layer atop the Martian core
Nature (2023)
-
Superionic effect and anisotropic texture in Earth’s inner core driven by geomagnetic field
Nature Communications (2023)
-
Primordial helium extracted from the Earth’s core through magnesium oxide exsolution
Nature Geoscience (2023)
-
Solubility of water in bridgmanite
Acta Geochimica (2023)