The origin of the terrestrial noble-gas signature

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In the atmospheres of Earth and Mars, xenon is strongly depleted relative to argon, when compared to the abundances in chondritic meteorites1, 2. The origin of this depletion is poorly understood3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. Here we show that more than one weight per cent of argon may be dissolved in MgSiO3 perovskite, the most abundant phase of Earth’s lower mantle, whereas the xenon solubility in MgSiO3 perovskite is orders of magnitude lower. We therefore suggest that crystallization of perovskite from a magma ocean in the very early stages of Earth’s history concentrated argon in the lower mantle. After most of the primordial atmosphere had been lost, degassing of the lower mantle replenished argon and krypton, but not xenon, in the atmosphere. Our model implies that the depletion of xenon relative to argon indicates that perovskite crystallized from a magma ocean in the early history of Earth and perhaps also Mars.

At a glance


  1. Scanning electron microscope images of MgSiO3 perovskite samples saturated with noble gases.
    Figure 1: Scanning electron microscope images of MgSiO3 perovskite samples saturated with noble gases.

    a, Perovskite crystallized in the presence of excess xenon. The bright spots in the image are xenon-filled bubbles in perovskite below the sample surface. However, in those parts of the perovskite crystals that are far away from bubbles, no xenon can be detected, implying very low xenon solubility (<100p.p.m.). b, Argon-saturated sample with perovskite (Pv, arrows) coexisting with MgSiO3 majorite (garnet structure, Maj). Dark spots are holes previously filled by argon gas. No argon can be detected in majorite (detection limit 150p.p.m.), but the perovskite contains 3,000p.p.m. of argon. c, Another sample, containing perovskite (lighter areas) coexisting with Mg2SiO4 ringwoodite (Rw, dark) and MgSiO3 ilmenite (Ilm, dark). d, X-ray map of argon distribution in the same sample as shown in c. Argon is only found in the perovskite phase. The concentration scale shown corresponds to the range from 0 (blue) to approximately 0.8wt% (green) of Ar.

  2. A lattice-strain model of noble-gas solubility in MgSiO3 perovskite.
    Figure 2: A lattice-strain model29 of noble-gas solubility in MgSiO3 perovskite.

    The fit is based on Ar, Kr and Xe solubility data for 25GPa at 1,600°C to 1,800°C. Estimated values for the solubilities of He and Ne are also shown. Fit parameters are the effective Young’s modulus Em = 35GPa; radius of the oxygen site ri = 1.4Å, and strain-free solubility c0 = 1.53wt%. Noble-gas radii are from ref. 22. Error bars are one standard deviation. For further details, see Supplementary Information.

  3. A sample containing phase X (phX) coexisting with MgSiO3 ilmenite (Ilm), SiO2 stishovite (St) and K2CO3 carbonate.
    Figure 3: A sample containing phase X (phX) coexisting with MgSiO3 ilmenite (Ilm), SiO2 stishovite (St) and K2CO3 carbonate.

    a, Scanning electron microscope image. b, X-ray map of argon distribution; argon is only present in phase X. The concentration scale shown corresponds to the range from 0 (blue) to approximately 1wt% (red) of Ar.


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  1. Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany

    • Svyatoslav S. Shcheka &
    • Hans Keppler


S.S.S. carried out all experiments and chemical analyses reported in this paper. H.K. suggested this study. Both authors wrote the manuscript together.

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    This file contains Supplementary Text and Data, Supplementary Figures 1-4, Supplementary Table 1 and additional references.

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