Origin of the Low Rigidity of the Earth's Inner Core

Belonoshko, Anatoly B.; Skorodumova, Natalia V.; Davis, Sergio; Осипцов, А. Н.; Rosengren, Anders; Johansson, Börje

doi:10.1126/science.1141374

Cited by 75 publications

(74 citation statements)

References 26 publications

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“…For example, it allows one to reproduce the structure of liquid iron [14]- [16] as well as its viscosity [7,17]. It also allows one to explain a number of features of IC [9,10]. The melting temperature of Fe at the pressure of the outer core-inner core boundary (330 GPa), according to the EAM, is consistent with the temperature computed from first principles [18] (later revised to a somewhat lower temperature) within the mutual error bars.…”

supporting

confidence: 62%

“…It was suggested, on the basis of non-empirical [6] molecular dynamics (MD) simulations, that under high pressure iron transforms on heating to the body-centered cubic (bcc) phase [7]. A number of IC properties can be explained within the paradigm of the bcc iron phase stability under the IC PT conditions, such as the low shear modulus [8,9] and elastic anisotropy [10]. However, computations performed by Vocadlo et al [11] have not confirmed the bcc stability.…”

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confidence: 99%

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Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation

et al. 2009

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confidence: 62%

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confidence: 99%

Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation

et al. 2009

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“…The time step was equal to 0.5 fs. The bcc elastic constants have been computed earlier (54). The hcp elastic constants have been calculated in the present work in a way similar to the approach applied by L. Vočadlo (55).…”

Section: Modelmentioning

confidence: 99%

Hemispherical anisotropic patterns of the Earth’s inner core

Mattesini

Belonoshko

Buforn

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling ∼3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core.elastic anisotropy | Fe-bcc/-hcp | PKiKP/PKIKP waves | molecular dynamics T he Earth's inner core (IC) is a small spherical body (with a radius of 1,200 km) located at the center of our home planet. Since its discovery in the late 1936 by Inge Lehmann (1), it has long been the most out of reach and enigmatic place of the Earth. Through comparison of the equation of state to seismic data and the abundance of iron, it has been established that the solid IC mainly consists of iron (2-4). The growth of the IC from the freezing of the molten iron alloy at the inner-core boundary (ICB) (5) drives the convection in the outer core and provides the energy source for the geodynamo (6). From the analysis of the normal modes of the Earth's free oscillations and the body wave data, it has been found that compressional P waves travel about 3% faster along the Earth's spin axis than in the equatorial plane (7-10). The growing evidence of an elastic anisotropic IC has continued to generate interesting understandings of the deepest part of our planet, though not all the scientific efforts have converged to the same scenario. Surprisingly, the picture has become more and more confusing as further observations have been collected (7). Explaining the anisotropic IC behavior within a unified and well-accepted geophysical model has become an increasingly complicated issue. Nowadays, we know that the Earth's inner core has a rather complex three-dimensional structure, where texture (11-13) and degree of seismic anisotropy (14-20) change considerably with depth. The most recent view of the solid core corresponds to an uppermost isotropic layer characterized by faster P waves in the eastern hemisphere than in the western one (15,21,22). Although the existence of an outermost isotropic layer has somewhat been questioned (23, 24), more consensus has been reached about the presence of a deeper and more anisotropic region (13,16,25).Different mechanisms have been proposed to explain the IC anisotropy (26, 27), though most of them have firmly relied on the lattice-preferred orientation (LPO) of both the hexagonalclose-packed (hcp) (12,(28)(29)(30)(31) and the body-centered-cubic (bcc) iron crystals (32...

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“…It is known that the resistance of pure iron to shear does not match the very low shear modulus of the Earth's inner core [4]. At 360 GPa pressure, Belonoshko et al calculated G=274.3 GPa at T =6000 K, and G=243.1…”

Section: Resultsmentioning

confidence: 99%

“…It is widely accepted, that iron is its main component, however there is no consensus about the crystal phase in which iron is present. In recent years, Fe was suggested to occur in the core in the body-centered cubic (bcc) phase [1,2,3,4,5]. It is known, however, that the density of pure Fe is larger than that of the inner core.…”

Section: Introductionmentioning

confidence: 99%

Thermo-physical properties of body-centered cubic iron–magnesium alloys under extreme conditions

Kádas

Ahuja

Johansson

et al. 2011

Solid State Communications

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This is an author produced version of a paper published in Solid State Communications. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. AbstractUsing density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C ′ ). Magnesium alloying significantly increases C ′ of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in details. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth's inner core as provided by seismic observations.

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Origin of the Low Rigidity of the Earth's Inner Core

Cited by 75 publications

References 26 publications

Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation

Quenching of bcc-Fe from high to room temperature at high-pressure conditions: a molecular dynamics simulation

Hemispherical anisotropic patterns of the Earth’s inner core

Thermo-physical properties of body-centered cubic iron–magnesium alloys under extreme conditions

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