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The primordial He budget of the Earth set by percolative core formation in planetesimals

A.S.G. Roth1,

1Institute of Geochemistry and Petrology, ETH Zurich, 8092 Zurich, Switzerland

C. Liebske1,

1Institute of Geochemistry and Petrology, ETH Zurich, 8092 Zurich, Switzerland

C. Maden1,

1Institute of Geochemistry and Petrology, ETH Zurich, 8092 Zurich, Switzerland

K.W. Burton2,

2Department of Earth Sciences, Durham University, Durham, UK

M. Schönbächler1,

1Institute of Geochemistry and Petrology, ETH Zurich, 8092 Zurich, Switzerland

H. Busemann1

1Institute of Geochemistry and Petrology, ETH Zurich, 8092 Zurich, Switzerland

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Roth, A.S.G., Liebske, C., Maden, C., Burton, K.W., Schönbächler, M., Busemann, H. (2019) The primordial He budget of the Earth set by percolative core formation in planetesimals. Geochem. Persp. Let. 9, 26–31.

The National Center for Competence in Research “PlanetS” supported by the Swiss National Science Foundation (SNSF).

Geochemical Perspectives Letters v9  |  doi: 10.7185/geochemlet.1901
Received 10 September 2018  |  Accepted 19 December 2018  |  Published 21 January 2019
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0




Table 1 Helium and Ne isotopic concentrations. The noble gas concentrations are in 10-10 cm3 STP/g (1 cm3 STP corresponds to 2.6868 × 1019 atoms). The 4He concentration in the olivine of the two-day experiment was not measured. The uncertainties are 2 sd and include only ion beam measurement uncertainties and sample mass uncertainties.
SampleDuration3He 4He22Ne20Ne/22Ne21Ne/22Ne
Olivine start. mat.10072±13367914±1204242.2±6.20.8557±0.00221.0419±0.0018
1200 °C
Olivine2 hours7.44±0.1481±122026.7±4.20.8390±0.00230.9712±0.0021
[FeS]2.607±0.04155.7±8.587.70±0.262.262±0.0850.8413±0.0038
Olivine1 day0.412±0.0227.3±3.1889.8±1.40.8534±0.00160.9763±0.0017
[FeS]4.361±0.09773.8±8.731.68±0.161.716±0.0180.8909±0.0059
Olivine2 days0.284±0.017-1034.8±2.40.8543±0.00300.9756±0.0026
[FeS]4.25±0.14100±2717.59±0.578.43±0.340.1677±0.0093
Olivine4 days0.776±0.03112±101407.7±2.00.8735±0.00350.9775±0.0017
[FeS]6.033±0.095180.8±4.913.87±0.249.19±0.180.1067±0.0039
Olivine6 days0.465±0.0137.1±3.21086.8±3.30.8460±0.00270.9781±0.0045
[FeS]7.18±0.1588.4±5.33.12±0.235.95±0.490.325±0.042
1450 °C
Olivine2 hours1.25±0.3219±12785.5±2.70.9629±0.00631.0245±0.0042
[FeS]18.37±0.55215±116.45±0.524.11±0.410.680±0.057
Olivine1 day0.82±0.1117.4±9.558.03±0.450.928±0.0421.0116±0.0088
[FeS]8.78±0.26116.2±9.46.76±0.387.02±0.570.413±0.026
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Figure 1 Helium and Ne isotopic compositions in the run products. Materials contain mixtures of atmospheric and cosmogenic noble gases. (a) Olivine-[FeS] pairs have within analytical uncertainties the same 3He/4He ratios except for the experiment conducted at 1200 °C for 2 hours. (b) All olivine-[FeS] pairs have different Ne isotopic compositions. Error bars are 2 sd.
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Figure 2 Metal-silicate (liquid-solid) partition coefficients for He. The dashed line shows the average partition coefficient DHe value of 11.8 (n = 11). The shaded area defines the two standard error of the mean (2 se) of 1.8. Data for the two-hour experiment are excluded and the 4He partition coefficient for the two-day experiment is missing. Uncertainties include only gas concentration uncertainties. Error bars are 2 sd.
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Figure 3 Helium concentration in the Earth’s early core and mantle as a function of the fraction of precursors’ cores equilibration with a terrestrial magma ocean. Mass balance calculations assume 1/3 metal and 2/3 silicate by mass and a He concentration in the bulk Earth that equals 1 (see Supplementary Information). Two scenarios are evaluated whereby metal and silicate (liquid-liquid) equilibrate in a shallow magma ocean (DHe = 0.001) and in a deep magma ocean (DHe = 0.01) (Bouhifd et al., 2013

Bouhifd, M.A., Jephcoat, A.P., Heber, V.S., Kelley, S.P. (2013) Helium in Earth’s early core. Nature Geoscience 6, 982-986.

). Datasets for the Earth’s early mantle overlap on the diagram. The inset shows the enrichment factor, i.e. the He concentration in the Earth’s early core at any fraction of equilibration relative to that assuming full (liquid-liquid) equilibrium. The shaded areas represent the range of equilibration from 0 to 36 %, for which geochemical models do not have satisfactory matches between siderophile element abundances and isotopic constraints (Rudge et al., 2010

Rudge, J.F., Kleine, T., Bourdon, B. (2010) Broad bounds on Earth’s accretion and core formation constrained by geochemical models. Nature Geoscience 3, 439-443.

).
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