An Experimental Perspective on the Light Element in Earth’s Core

Hillgren, V. J.; Geßmann, C. K.; Li, J.

doi:10.2307/j.ctv1v7zdrp.20

Cited by 52 publications

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“…Si/Fe is only decreased to be comparable to bulk Earth, if bulk Earth contains 10% silicon in the core (e.g. Hillgren et al, 2000;Ricolleau et al, 2011), but which may be unrealistically high (Badro et al, 2014). In this case a protoplanet with the composition of bulk Earth lies to the extreme of the distribution of protoplanets produced in our simulations.…”

Section: Discussionmentioning

confidence: 86%

“…Given the uncertainity in the composition of light elements in Earth's core (e.g. Hillgren et al, 2000;Ricolleau et al, 2011), we can reasonably conclude that it is just possible to produce a protoplanet with Earth's Mg/Fe and Si/Fe ratios, from chondritic material, due to collisional erosion of differentiated planetesimals during the early stages of planet formation. This work, however, is only able to produce a protoplanet of Earth's non-chondritic composition, if Earth happens to be a special case, falling right to one extreme of the distribution of protoplanets that might be formed in this manner, and with a core containing a very high and possibly unrealistic silicon content.…”

Section: Discussionmentioning

confidence: 87%

“…In the second scenario, 10% of the mass of the core is assumed to be entirely silicon. This is a reasonable upper limit on the potential silicon content of the core (Hillgren et al, 2000;Ricolleau et al, 2011). However, the recent work of Badro et al (2014) indicate that density and sound velocities calculated for core-forming alloys constrain Si contents to ∼ 5% or less in Earth's core.…”

Section: Tracking Mg/fe and Si/fe In The Protoplanetsmentioning

confidence: 83%

“…The seismologically constrained density deficity requires the Earth's core to contain ∼ 10% light elements (e.g. Birch, 1964;Poirier, 1994;Allègre et al, 1995;Hillgren et al, 2000). We consider two extreme possibilities to match this constraint.…”

Section: Tracking Mg/fe and Si/fe In The Protoplanetsmentioning

confidence: 99%

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A collisional origin to Earth’s non-chondritic composition?

Bonsor

Leinhardt

Carter

et al. 2015

Icarus

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Several lines of evidence indicate a non-chondritic composition for Bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142 Nd/ 144 Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (> 100 km) up to isolation mass (> 0.16 M ⊕ ). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.

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Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 87%

Section: Tracking Mg/fe and Si/fe In The Protoplanetsmentioning

confidence: 83%

Section: Tracking Mg/fe and Si/fe In The Protoplanetsmentioning

confidence: 99%

See 2 more Smart Citations

A collisional origin to Earth’s non-chondritic composition?

Bonsor

Leinhardt

Carter

et al. 2015

Icarus

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“…Tingle [ 10] proposed that carbon has been incorporated in the core during its formation, and as supporting evidence used the observed large amounts of carbon in iron meteorites, as well as experiments on its high-pressure solubility in liquid iron [ 9,11]. Estimates of carbon content in the inner core range from 0.2 wt.% [ 12] to 4 wt.% [ 13]. Anisichkin [ 14], based on shock-wave and seismic data, advocated carbon as a major light element (as much as 10 wt%) in the core, partly in the diamond phase.…”

Section: Introductionmentioning

confidence: 91%

Fe–C and Fe–H systems at pressures of the Earth's inner core

Bazhanova¹,

Oganov²,

Gianola³

2012

Phys.-Usp.

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The solid inner core of the Earth is predominantly composed of iron alloyed with several percent Ni and some lighter elements, Si, S, O, H, and C being the prime candidates. To establish the chemical composition of the inner core it is necessary to find the range of compositions that can explain its observed characteristics. Recently, there have been a growing number of papers investigating C and H as possible light elements in the core, but the results are contradictory. Here, using ab initio simulations, we study the Fe-C and Fe-H systems at inner core pressures (330-364 GPa). Using the evolutionary structure prediction algorithm USPEX, we have determined the lowest-enthalpy structures of possible carbides (FeC, Fe 2 C, Fe 3 C, Fe 4 C, FeC 2 , FeC 3 , FeC 4 and Fe 7 C 3 ) and hydrides (Fe 4 H, Fe 3 H, Fe 2 H, FeH, FeH 2 , FeH 3 , FeH 4 ) and have found that Fe 2 C (space group Pnma) is the most stable iron carbide at pressures of the inner core, while FeH, FeH 3 and FeH 4 are stable iron hydrides at these conditions. For Fe 3 C, the cementite structure (space group Pnma) and the Cmcm structure recently found by random sampling are less stable than the I-4 and C2/m structures found here. We have found that FeH 3 and FeH 4 adopt chemically interesting thermodynamically stable structures, in both compounds containing trivalent iron. We find that the density of the inner core can be matched with a reasonable concentration of carbon, 11-15 mol % (2.6-3.7 wt. %) at relevant pressures and temperatures. This concentration matches that in CI carbonaceous chondrites and corresponds to the average atomic mass in the range 49.3-51.0, in close agreement with inferences from the Birch's law for the inner core. Similarly made estimates for the maximum hydrogen content are unrealistically high, 17-22 mol.% (0.4-0.5 wt. %), which corresponds to the average atomic mass in the range 43.8-46.5. We conclude that carbon is a better candidate light alloying element than hydrogen.

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Shock compression of Fe‐Ni‐Si system to 280 GPa: Implications for the composition of the Earth's outer core

Zhang

Sekine

et al. 2014

Geophysical Research Letters

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The shock Hugoniot of an Fe-9 wt %Ni-10 wt %Si system as a model of the Earth's core has been measured up to~280 GPa using a two-stage light-gas gun. The samples had an average density of 6.853 (±0.036) g/cm 3 . The relationship between shock velocity (U s ) and particle velocity (u p ) can be described by U s (km/s) = 3.95 (±0.15) + 1.53 (±0.05) u p (km/s). The calculated Hugoniot temperatures and the melting curve indicate that the model composition melts above a shock pressure of~168 GPa, which is significantly lower than the shock-melting pressure of iron (~225 GPa). A comparison of the pressure-density (P-ρ) profiles between the model composition and the preliminary reference Earth model gives a silicon content close to 10 wt %, necessary to compensate the density deficit in the Earth's outer core from seismological observations, if silicon is present as a major light element in the Fe-Ni core system.

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An Experimental Perspective on the Light Element in Earth’s Core

Cited by 52 publications

References 0 publications

A collisional origin to Earth’s non-chondritic composition?

A collisional origin to Earth’s non-chondritic composition?

Fe–C and Fe–H systems at pressures of the Earth's inner core

Shock compression of Fe‐Ni‐Si system to 280 GPa: Implications for the composition of the Earth's outer core

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