Accretion of the Earth

Canup, R. M.

doi:10.1098/rsta.2008.0101

Cited by 72 publications

(60 citation statements)

References 38 publications

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“…The parameters that are the most poorly constrained and strongly influence the calculations (also see [132]) are the degree of equilibration between the impactor core and proto-Earth mantle (k), the metal-silicate partition coefficient for W during lunar core formation (D M ) and the fraction of the Moon that came from the impactor versus the proto-Earth mantle (h). For this reason, we present a range of simulations by varying k, D and h over acceptable ranges (0 < k < 0.4 [134,135]; 50 < D < 100 [128,136]; 0.5 < h < 0.9 [9,137]). …”

Section: Hf-w In the Earth-moon-impactor Systemmentioning

confidence: 99%

Geochemical arguments for an Earth-like Moon-forming impactor

Dauphas

Burkhardt

Warren

et al. 2014

Phil. Trans. R. Soc. A.

128

101

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Geochemical evidence suggests that the material accreted by the Earth did not change in nature during Earth's accretion, presumably because the inner protoplanetary disc had uniform isotopic composition similar to enstatite chondrites, aubrites and ungrouped achondrite NWA 5363/5400. Enstatite meteorites and the Earth were derived from the same nebular reservoir but diverged in their chemical evolutions, so no chondrite sample in meteorite collections is representative of the Earth's building blocks. The similarity in isotopic composition (Δ 17 O, ε 50 Ti and ε 54 Cr) between lunar and terrestrial rocks is explained by the fact that the Moon-forming impactor came from the same region of the disc as other Earth-forming embryos, and therefore was similar in isotopic composition to the Earth. The heavy δ 30 Si values of the silicate Earth and the Moon relative to known chondrites may be due to fractionation in the solar nebula/protoplanetary disc rather than partitioning of silicon in Earth's core. An inversion method is presented to calculate the Hf/W ratios and ε 182 W values of the proto-Earth and impactor mantles for a given Moon-forming impact scenario. The similarity in tungsten isotopic composition between lunar and terrestrial rocks is a coincidence that can be explained in a canonical giant impact scenario if an early formed embryo (two-stage model age of 10–20 Myr) collided with the proto-Earth formed over a more protracted accretion history (two-stage model age of 30–40 Myr).

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Section: Hf-w In the Earth-moon-impactor Systemmentioning

confidence: 99%

Geochemical arguments for an Earth-like Moon-forming impactor

Dauphas

Burkhardt

Warren

et al. 2014

Phil. Trans. R. Soc. A.

128

101

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“…The Moon is thought to have formed from the re-accretion of hot material originating from the mantle of a Mars-sized impactor that struck the Earth (e.g. Canup, 2008). From an isotopic point of view, the two key aspects of this story are that: 1) the impactor was differentiated prior to encountering the Earth; and that 2) the bulk of the Moon was derived from impactor mantle material.…”

Section: Introductionmentioning

confidence: 99%

“…However, because numerical studies show that up to 40% of the Moon may be derived from the target (Canup, 2008), in Section 3.3 we investigate the effect of adding target material to the proto-Moon.…”

Section: Approach and Assumptionsmentioning

confidence: 99%

Tungsten isotopic evolution during late-stage accretion: Constraints on Earth–Moon equilibration

Nimmo

O’Brien

Kleine

2010

Earth and Planetary Science Letters

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We couple the results of N-body simulations of late-stage accretion (O'Brien et al. 2006) to a hafnium-tungsten (Hf-W) isotopic evolution code to investigate the evolution of planetary bodies in the inner solar system. Simulations can simultaneously produce planets having Earth-and Mars-like masses and Hf-W systematics by assuming that the tungsten partition coefficient decreases with increasing semi-major axis (e.g. due to increasing oxidation). Simulations assuming that Jupiter and Saturn occupy circular orbits are more successful at reproducing the Hf-W systematics than those assuming presentday Jupiter and Saturn orbits. To generate Earth-like tungsten anomalies, 30-80% of each impactor core is required to re-equilibrate with the target mantle. Some model outcomes yield a target and final impactor having similar (Earth-and Moon-like) tungsten anomalies. However, in no case can the inferred lunar Hf/W ratio be simultaneously matched. This result suggests that the Moon isotopically equilibrated with the Earth's mantle in the aftermath of the giant impact (cf. Pahlevan and Stevenson 2007). Alternatively, either the dynamical models which show the Moon being derived primarily from the impactor mantle, or the accretion timescales obtained by the N-body simulations, are incorrect.

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“…In the more detailed giant impactor simulations that indicate the extent of planetary-scale vaporization, melting and material dispersal before re-accretion (Canup 2004(Canup , 2008, it is perhaps a question of whether or not we would expect to find any volatiles trapped within the solid planets at all. However, we do, and an important additional clue to planetary volatile origin lies in the isotopic and elemental composition of the noble gases degassing from the solid Earth today.…”

Section: Introductionmentioning

confidence: 99%

What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Ballentine

Holland²

2008

Phil. Trans. R. Soc. A.

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Study of commercially produced volcanic CO 2 gas associated with the Colorado Plateau, USA, has revealed substantial new information about the noble gas isotopic composition and elemental abundance pattern of the mantle. Combined with published data from midocean ridge basalts, it is now clear that the convecting mantle has a maximum 20 Ne/ 22 Ne isotopic composition, indistinguishable from that attributed to solar wind-implanted (SWI) neon in meteorites. This is distinct from the higher 20 Ne/ 22 Ne isotopic value expected for solar nebula gases. The non-radiogenic xenon isotopic composition of the well gases shows that 20 per cent of the mantle Xe is 'solar-like' in origin, but cannot resolve the small isotopic difference between the trapped meteorite 'Q'-component and solar Xe. The mantle primordial 20 Ne/ 132 Xe is approximately 1400 and is comparable with the upper end of that observed in meteorites. Previous work using the terrestrial 129 I-129 Xe mass balance demands that almost 99 per cent of the Xe (and therefore other noble gases) has been lost from the accreting solids and that Pu-I closure age models have shown this to have occurred in the first ca 100 Ma of the Earth's history. The highest concentrations of Q-Xe and solar wind-implanted (SWI)-Ne measured in meteorites allow for this loss and these high-abundance samples have a Ne/Xe ratio range compatible with the 'recycled-aircorrected' terrestrial mantle. These observations do not support models in which the terrestrial mantle acquired its volatiles from the primary capture of solar nebula gases and, in turn, strongly suggest that the primary terrestrial atmosphere, before isotopic fractionation, is most probably derived from degassed trapped volatiles in accreting material.By contrast, the non-radiogenic argon, krypton and 80 per cent of the xenon in the convecting mantle have the same isotopic composition and elemental abundance pattern as that found in seawater with a small sedimentary Kr and Xe admix. These mantle heavy noble gases are dominated by recycling of air dissolved in seawater back into the mantle. Numerical simulations suggest that plumes sampling the core-mantle boundary would be enriched in seawater-derived noble gases compared with the convecting mantle, and therefore have substantially lower 40 Ar/ 36 Ar. This is compatible with observation. The subduction process is not a complete barrier to volatile return to the mantle.

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Accretion of the Earth

Cited by 72 publications

References 38 publications

Geochemical arguments for an Earth-like Moon-forming impactor

Geochemical arguments for an Earth-like Moon-forming impactor

Tungsten isotopic evolution during late-stage accretion: Constraints on Earth–Moon equilibration

What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

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Accretion of the Earth

Cited by 72 publications

References 38 publications

Geochemical arguments for an Earth-like Moon-forming impactor

Geochemical arguments for an Earth-like Moon-forming impactor

Tungsten isotopic evolution during late-stage accretion: Constraints on Earth–Moon equilibration

What CO 2 well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

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Resources

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What CO ₂ well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere