Letter | Published:

Magnesium isotope evidence that accretional vapour loss shapes planetary compositions

Nature volume 549, pages 511515 (28 September 2017) | Download Citation

Abstract

It has long been recognized that Earth and other differentiated planetary bodies are chemically fractionated compared to primitive, chondritic meteorites and, by inference, the primordial disk from which they formed. However, it is not known whether the notable volatile depletions of planetary bodies are a consequence of accretion1 or inherited from prior nebular fractionation2. The isotopic compositions of the main constituents of planetary bodies can contribute to this debate3,4,5,6. Here we develop an analytical approach that corrects a major cause of measurement inaccuracy inherent in conventional methods, and show that all differentiated bodies have isotopically heavier magnesium compositions than chondritic meteorites. We argue that possible magnesium isotope fractionation during condensation of the solar nebula, core formation and silicate differentiation cannot explain these observations. However, isotopic fractionation between liquid and vapour, followed by vapour escape during accretionary growth of planetesimals, generates appropriate residual compositions. Our modelling implies that the isotopic compositions of magnesium, silicon and iron, and the relative abundances of the major elements of Earth and other planetary bodies, are a natural consequence of substantial (about 40 per cent by mass) vapour loss from growing planetesimals by this mechanism.

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Acknowledgements

We thank the Natural History Museum in London, NASA (National Aeronautics and Space Administration), O. Nebel, D. Ionov, S. Nielsen, E. Takazawa, K. Sims, Y. Niu, R. Brooker and C. Robinson for supplying us with various samples. We acknowledge C. Bierson for his help with direct outflow vapour loss modelling. This study was funded by NERC grant NE/L007428/1 to T.E., C.D.C. and M.J.W., which was motivated by NE/C0983/1. ERC Adv Grant 321209 ISONEB further supported the work of T.E. and C.D.C. NERC grant NE/K004778/1 to Z.M.L. funded P.J.C.

Author information

Author notes

    • Philip J. Carter
    • , Yi-Jen Lai
    •  & Matthias Willbold

    Present addresses: Department of Earth and Planetary Sciences, University of California, Davis, One Shields Avenue, Davis, California 95616, USA (P.J.C.); Macquarie University GeoAnalytical, Department of Earth and Planetary Sciences, Macquarie University, 12 Wally’s Walk, Sydney, New South Wales 2109, Australia (Y.-J.L.); Geowissenschaftliches Zentrum Göttingen (GZG), University of Göttingen, Goldschmidtstrasse 1, 37077 Göttingen, Germany (M.W.).

Affiliations

  1. School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK

    • Remco C. Hin
    • , Christopher D. Coath
    • , Yi-Jen Lai
    • , Philip A. E. Pogge von Strandmann
    • , Matthias Willbold
    • , Michael J. Walter
    •  & Tim Elliott
  2. School of Physics, University of Bristol, H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, UK

    • Philip J. Carter
    •  & Zoë M. Leinhardt
  3. Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, California 95064, USA

    • Francis Nimmo
  4. London Geochemistry and Isotope Centre, Department of Earth Sciences, University College London, and Department of Earth and Planetary Sciences, Birkbeck, University of London, Gower Street, London WC1E 6BT, UK

    • Philip A. E. Pogge von Strandmann

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Contributions

All data presented were measured by R.C.H. R.C.H. and C.D.C. performed vapour–liquid modelling. P.J.C. was responsible for calculations relating to N-body simulations. F.N. modelled the direct outflow vapour loss mechanism. R.C.H. and T.E. wrote the manuscript. C.D.C., Y.-J.L., P.A.E.P.v.S. and M.W. were involved in measurements in the initial stages of this study. All authors read and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Remco C. Hin.

Reviewer Information Nature thanks F. Moynier and E. Young for their contribution to the peer review of this work.

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    Supplementary Data

    This file contains source data for Table 1 (Magnesium isotope compositions of chondrites, terrestrial (ultra-)mafics, and achondrites).

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https://doi.org/10.1038/nature23899

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