Skip to main content
SpringerLink
Log in

New Views of the Earth’s Inner Core from Computational Mineral Physics

  • Chapter
  • First Online:
New Frontiers in Integrated Solid Earth Sciences

Part of the book series: International Year of Planet Earth ((IYPE))

Abstract

Although one third of the mass of our planet resides in its metallic core (divided into a molten outer part and a solid inner part), fundamental properties such as its chemical composition and internal structure remain poorly known. Although it is well established that the inner core consists of iron with some alloying lighter element(s), the crystal structure of the iron and the nature and concentrations of the light element(s) involved remain controversial. Seismologists, by studying the propagation characteristics of primary earthquake waves (P-waves), have shown that the inner core is anisotropic and layered, but the origins of these properties are not understood. Seismically observed shear waves (S-waves) add to the complexity as they show unexpectedly low propagation velocities through the inner core.

Interpretation of these seismic observations is hampered by our lack of knowledge of the physical properties of core phases at core conditions. In addition, the accuracy of derived inner core seismic properties is limited by the need to de-convolve inner core observations from seismic structure elsewhere in the Earth. This is particularly relevant in the case of shear waves where detection is far from straightforward. A combination of well-constrained seismological data and accurate high-pressure, high-temperature elastic properties of candidate core materials would allow for a full determination of the structure and composition of the inner core - an essential prerequisite to understanding Earth’s differentiation and evolution.

Unfortunately, the extreme conditions of pressure (up to 360 GPa or 3.6 million times atmospheric pressure) and temperature (up to 6000 K) required make results from laboratory experiments unavoidably inconclusive at present. An alternative and complementary approach, that has only recently become available, is computational mineral physics, which uses computer simulations of materials at inner core conditions. Ab initio molecular dynamics simulations have been used to determine the stable phase(s) of iron in the Earth’s core and to calculate the elasticity of iron and iron alloys at core conditions. Calculated S-wave velocities are significantly higher than those inferred from seismology. If the seismological observations are robust, a possible explanation for this discrepancy is that the inner core contains a significant amount of melt (possibly >10%). The observed anisotropy can only be explained by almost total alignment of inner core crystals.

This is a preview of subscription content, log in via an institution to check access.

Access this chapter

Log in via an institution
Chapter
USD 29.95
Price excludes VAT (USA)
  • Available as PDF
  • Read on any device
  • Instant download
  • Own it forever
eBook
USD 84.99
Price excludes VAT (USA)
  • Available as EPUB and PDF
  • Read on any device
  • Instant download
  • Own it forever
Softcover Book
USD 109.99
Price excludes VAT (USA)
  • Compact, lightweight edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info
Hardcover Book
USD 109.99
Price excludes VAT (USA)
  • Durable hardcover edition
  • Dispatched in 3 to 5 business days
  • Free shipping worldwide - see info

Tax calculation will be finalised at checkout

Purchases are for personal use only

Institutional subscriptions

References

  • Ahrens TJ, Holland KG, Chen GQ 2002 Phase diagram of iron, revised core temperatures. Geophys. Res. Lett., 29, #1150.

    Article  Google Scholar 

  • Alfè D 2005 Melting curve of MgO from first principles simulations. Phys. Rev. Lett., 94, #235701.

    Article  Google Scholar 

  • Alfè D, Gillan MJ, Vočadlo L, Brodholt JP, Price GD 2002 The ab initio simulation of the Earth’s core. Phil. Trans. Royal Soc. A, 360, 1227–1244.

    Article  Google Scholar 

  • Antonangeli D, Occelli F, Requardt H 2004 Elastic anisotropy in textured hcp-iron to 112 GPa from sound wave propagation measurements. Earth Planet. Sci. Lett., 225, 243–251.

    Article  Google Scholar 

  • Badro J, Fiquet G, Guyot F, Gregoryanz E, Occelli F, Antonangeli D, Requardt E, Mermet A, D’Astuto M, Krisch M 2007 Effect of light elements on the sounds velocities in solid iron: Implications for the composition of the Earth’s core. Earth Planet. Sci. Lett., 254, 233.

    Article  Google Scholar 

  • Beghein C, Trampert J 2003 Robust normal mode constraints on inner core anisotropy from model space search. Science, 299, 552–555.

    Article  Google Scholar 

  • Birch F 1964 Density and composition of the mantle and core. J. Geophys. Res., 69, 4377–4388.

    Article  Google Scholar 

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

    Article  Google Scholar 

  • Boehler R, Ross M 1997 Melting curve of aluminium in a diamond anvil cell to 0.8 Mbar: Implications for iron. Earth Planet. Sci. Lett., 153, 223–227.

    Article  Google Scholar 

  • Brockhouse BN, Abou-Helal HE, Hallman ED 1967 Solid Stare Commun. 5, 211.

    Article  Google Scholar 

  • Brodholt J, Vočadlo L 2006 Applications of density functrional theory in the geosciences. MRS Bull., 31, 675–680.

    Google Scholar 

  • Brown JM, McQueen RG 1986 Phase transitions, Grüneisen parameter and elasticity of shocked iron between 77 GPa abd 400 GPa. J. Geophys. Res., 91, 7485–7494.

    Article  Google Scholar 

  • Cohen RE, Stixrude L, Wasserman E 1997 Tight-binding computations of elastic anisotropy of Fe, Xe, and Si under compression. Phys. Rev. B 56, 8575–8589. (errata, Phys.Rev. B 58 (1997) 5873).

    Article  Google Scholar 

  • Collerson KD, Hpaugoda S, Kamber BS, Williams Q 2000 Rocks from the mantle transition zone: Majorite-bearing xenoliths from Malaita, southwest Pacific. Science, 288, 1215–1223.

    Article  Google Scholar 

  • Côté AS, Vočadlo L, Brodholt J 2008a The effect of silicon impurities on the phase diagram of iron and possible implications for the Earth’s core structure. J. Phys. Chem. Solids, 69, 9, 2177–2181.

    Google Scholar 

  • Côté AS, Vočadlo L, Brodholt J 2008b Light elements in the core: Effects of impurities on the phase diagram of iron. Geophys. Res. Lett., 35, L05306.

    Article  Google Scholar 

  • Côté AS, Vočadlo L, Alfe D, Brodholt J 2009 Ab initio calculations on the combined effect of temperature and silicon on the stability of different iron phases in the Earth’s inner core. Submitted.

    Google Scholar 

  • Creager KC 1992 Anisotropy of the inner core from differential travel times of the phases PKP and PKIKP. Nature, 356, 309–314.

    Article  Google Scholar 

  • Dobson DP, Vočadlo L, Wood IG 2002 A new high pressure phase of FeSi. Am. Min., 87, 784–787.

    Google Scholar 

  • Dziewonski AM, Anderson DL 1981 Preliminary reference Earth model. Phys. Earth Planet. Int., 25, 297–356.

    Article  Google Scholar 

  • Hanstrom A, Lazor P 2000 High pressure melting and equation of state of aluminium. J. Alloys Comp., 305, 209–215.

    Article  Google Scholar 

  • Hashin Z, Shtrikman S 1963 A variational approach to the theory of the elastic behaviour of multiphase materials. J. Mech. Phys. Solids, 11, 127.

    Article  Google Scholar 

  • Hohenberg P, Kohn W 1964 Inhomogeneous electron gas. Phys. Rev., 136, B864–B871.

    Article  Google Scholar 

  • Ishii M, Dziewonski AM 2003 Distinct seismic anisotropy at the centre of the Earth. Phys. Earth Planet. Int., 140, 203–217.

    Article  Google Scholar 

  • Jackson I, Fitz Gerald JD, Kokkonen H 2000 High temperature viscoelastic relaxation in iron and its implications for the shear modulus and attenuation of the Earth’s inner core. J. Geophys. Res. B10, 23, 605–23634.

    Google Scholar 

  • Kresse G and Furthmüller J 1996 Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186.

    Google Scholar 

  • Kuwayama Y, Hirose K, Nagayoshi S, Ohishi Y 2008 Phase relations of iron and iron-nickel alloys up to 300 GPa: Implications for the composition and structure of the inner core. Earth Planet. Sci. Lett., 273, 379–385.

    Article  Google Scholar 

  • Laio A, Bernard S, Chiarotti GL, Scandolo S, Tosatti E 2000 Physics of iron at Earth’s core conditions. Science, 287, 1027–1030.

    Article  Google Scholar 

  • Lin JF, Heinz DL, Campbell AJ, Devine JM, Shen GY 2002 Iron-silicon alloy in the Earth’s core?. Science, 295, 313–315.

    Article  Google Scholar 

  • Liu L 1979 The Earth: Its origin, structure and evolution. Ed. MW McElhinny, 177–202, Academic, New York.

    Google Scholar 

  • Ma Y, Somayazulu M, Shen G, Mao HK, Shu J, Hemley RJ 2004 In situ X-ray diffraction studies of iron to Earth-core conditions. Phys. Earth Planet Int., 143–144, 455–467.

    Article  Google Scholar 

  • Mao HK, Wu Y, Chen LC, Shu JF, Jephcoat AP 1990 Static compression of iron to 300 GPa and Fe0.8Ni0.2 alloy to 260 GPa – implications for composition of the core. J. Geophys. Res., 95, 21737–21742.

    Article  Google Scholar 

  • Mainprice D 1990 A Fortran program to calculate seismic anisotropy from the lattice preferred orientation of minerals. Comput. Gesosci. 16, 385. (http://ftp://www.gm.univ-montp2.fr/mainprice//CareWare_Unicef_Programs/).

    Article  Google Scholar 

  • Masters G, Gubbins D 2003 On the resolution of density within the Earth. Phys. Earth Planet. Int., 140, 159–167.

    Article  Google Scholar 

  • McDonough WF, Sun S-S 1995 The composition of the Earth. Chem. Geol., 120, 223–253.

    Article  Google Scholar 

  • Mikhaylushkin AS, Simak SI, Dubrovinsky L, Dubrovinskaia N, Johansson B, Abrikosov IA 2007 Pure iron compressed and heated to extreme conditions. Phys. Rev. Lett., 99, 165505.

    Article  Google Scholar 

  • Nguyen JH, Holmes NC 2004 Melting of iron at the physical conditions of the Earth’s core. Nature, 427, 339–342.

    Google Scholar 

  • Oganov AR, Brodholt JP, Price GD 2001 The elastic constants of MgSiO3 perovskite at pressures and temperatures of the Earth’s mantle. Nature, 411, 934–937.

    Article  Google Scholar 

  • Oreshin SI, Vinnik LP 2004 Heterogeneity and anisotropy of seismic attenuation in the inner core. Geophys. Res. Lett., 31, #L02613.

    Article  Google Scholar 

  • Ouzounis A, Creager KC 2001 Isotropy overlying anisotropy at the top of the inner core. Geophys. Res. Lett., 28, 4221–4334.

    Article  Google Scholar 

  • Poirier JP 1994 Light elements in the Earth’s outer core: A critical review. Phys. Earth Planet. Int., 85, 319–337.

    Article  Google Scholar 

  • Rama Murthy V, van Westrenen W, Fei Y 2003 Experimental evidence that potassium is a substantial radioactive heat source in planetary cores. Nature, 423, 163–165.

    Article  Google Scholar 

  • Resovsky J, Trampert J, Van der Hilst RD 2005 Error bars for the global seismic Q profile. Earth Planet. Sci. Lett., 230, 413–423.

    Article  Google Scholar 

  • Ringwood AE 1975 Composition and petrology of the Earth’s mantle. McGraw-Hill, New York.

    Google Scholar 

  • Sata N, Ohfuji H, Kobayashi H, Ohishi Y, Hirao N 2008 New high-pressure B2 phase of FeS above 180 GPa. Am. Min., 93, 492–494.

    Article  Google Scholar 

  • Shaner JW, Brown JM, McQueen RG 1984 in High Pressure in Science and Technology, edited by C Homan, RK Mac-Crone, and E Whalley, North Holland, Amsterdam, p. 137.

    Google Scholar 

  • Shearer P, Masters G 1990 The density and shear velocity contrast at the inner core boundary. Geophys. J. Int., 102, 491–498.

    Article  Google Scholar 

  • Shen GY, Mao HK, Hemley RJ, Duffy TS, Rivers ML 1998 Melting and crystal structure of iron at high pressures and temperatures. Geophys. Res. Lett., 25, 373–376.

    Article  Google Scholar 

  • Söderlind P, Moriarty JA, Wills JM 1996 First principles theory of iron up to earth’s core pressures: structural, vibrational and elastic properties. Phys. Rev. B, 53, 14063–14072.

    Article  Google Scholar 

  • Song X 1997 Anisotropy of the Earth’s inner core. Rev. Geophys., 35, 297–313.

    Article  Google Scholar 

  • Song XD, Helmberger DV 1993 Anisotropy of Earth’s inner core. Geophys. Res. Lett., 20, 2591–2594.

    Article  Google Scholar 

  • Song XD, Helmberger DV 1998 Seismic evidence for an inner core transition zone. Science, 282, 924–927.

    Article  Google Scholar 

  • Song XD, Xu XX 2002 Inner core transition zone and anomalous PKP(DF) waveforms from polar paths. Geophys. Res. Lett., 29, #1042.

    Article  Google Scholar 

  • Stixrude L, Cohen RE 1995 Constraints on the crystalline structure of the inner core – mechanical stability of bcc iron at high pressure. Geophys. Res. Lett., 22, 125–128.

    Article  Google Scholar 

  • Sun XL, Song XD 2002 PKP travel times at near antipodal distances: implications for inner core anisotropy and lowermost mantle structure. Earth Planet Sci. Lett., 199, 429–445.

    Article  Google Scholar 

  • Sun X, Song X 2008 The inner core of the Earth: texturing of iron crystals from three-dimensional seismic anisotropy. Earth Planet. Sci. Lett., 269, 56–65.

    Article  Google Scholar 

  • Vočadlo L 2007 Ab initio calculations of the elasticity of iron and iron alloys at inner core conditions: Evidence for a partially molten inner core. Earth Planet. Sci. Lett., 254, 227.

    Article  Google Scholar 

  • Vočadlo L, Dobson DP, Wood IG 2006 Ab initio study of nickel substitution into iron. Earth Plant. Sci. Lett., 248, 132–137.

    Article  Google Scholar 

  • Vočadlo L, Alfe D 2002 Ab initio melting curve of the fcc phase of aluminium. Phys. Rev. B 65, 214105, 1–12.

    Google Scholar 

  • Vočadlo L, Alfe D, Gillan MJ, Wood IG, Brodholt JP, Price GD 2003a Possible thermal and chemical stabilisation of body-centred-cubic iron in the Earth’s core. Nature, 424, 536–539.

    Article  Google Scholar 

  • Vočadlo L, Alfe D, Gillan MJ, Price GD 2003b The properties of iron under core conditions from first principles calculations. Phys. Earth Planet. Int., 140, 101–125.

    Article  Google Scholar 

  • Vočadlo L, Brodholt JP, Alfe D, Gillan MJ, Price GD 2000 Ab initio free energy calculations on the polymorphs of iron at core conditions. Phys. Earth Planet. Int., 117, 123–137.

    Article  Google Scholar 

  • Vočadlo L, Wood IG, Alfè D, Price GD 2008 Ab initio calculations on the free energy and high P-T elasticity of face-centred-cubic iron. Earth Planet. Sci. Lett., 268, 444–449.

    Article  Google Scholar 

  • Vočadlo L, Wood IG, Price GD 1999 Crystal structure, compressibility and possible phase transitions in epsilon-FeSi studied by first-principles pseudopotential calculations. Acta Cryst. B, 55, 484–493.

    Article  Google Scholar 

  • Vočadlo L, de Wijs G, Kresse G, Gillan MJ, Price GD 1997 First principles calculations on crystalline and liquid iron at earth’s core conditions. Faraday Discuss 106, ‘Solid-State Chemistry – New Opportunities from Computer Simulations’, 205–217.

    Article  Google Scholar 

  • Wang J-T, Wang D-S 2006 Finite temperature magnetism of tetragonal iron. Appl. Phys. Lett., 88, 132513.

    Article  Google Scholar 

  • Williams Q, Jeanloz R, Bass J, Svendsen B, Ahrens TJ 1987 The melting curve of iron to 250 Gigapascals: a constraint on the temperature at the Earth’s centre. Science, 236, 181–182.

    Article  Google Scholar 

  • Yoo CS, Holmes NC, Ross M, Webb DJ, Pike C 1993 Shock temperature and melting of iron at Earth’s core conditions. Phys. Rev. Lett., 70, 3931–3934.

    Article  Google Scholar 

Download references

Acknowledgements

LV would like to that Alex Côté and Dario Alfè for Figs. 2 and 11 respectively; LV would also like to thank Ian Wood for helpful comments on the manuscript. Much of this research was funded by the Royal Society through their University Research Fellowship scheme.

Author information

Authors and Affiliations

  1. Department of Earth Sciences, UCL, WC1E 6BT, London, UK

    Lidunka Vočadlo

Authors
  1. Lidunka Vočadlo
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Lidunka Vočadlo .

Editor information

Editors and Affiliations

  1. Faculteit Aardwetenschappen, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands

    S. Cloetingh

  2. GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473, Germany

    Jorg Negendank

Rights and permissions

Reprints and permissions

Copyright information

© 2009 Springer Science+Business Media B.V.

About this chapter

Cite this chapter

Vočadlo, L. (2009). New Views of the Earth’s Inner Core from Computational Mineral Physics. In: Cloetingh, S., Negendank, J. (eds) New Frontiers in Integrated Solid Earth Sciences. International Year of Planet Earth. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-2737-5_12

Download citation

Publish with us

Policies and ethics

Search

Navigation