Research ArticleGEOCHEMISTRY

Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact

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Science Advances  23 Jan 2019:
Vol. 5, no. 1, eaau3669
DOI: 10.1126/sciadv.aau3669
  • Fig. 1 Experimentally determined N contents and C solubilities as a function of S contents in Fe-Ni alloy melts.

    (A) The N content in the alloy melt is not significantly affected by the presence of S. The N content does not show a significant change between experiments with S-free and low S-bearing (~12 to 15 wt %) alloy melts for a given P-T condition, while it drops by 50% for high S-bearing (~21 to 28 wt %) alloys. The N content in a C-free system (29) is higher than that in a C-present system in this study and previous studies (12, 63). (B) The C solubility in the alloy melt decreases steadily with an increasing S content in the alloy melt with an order of magnitude difference between S-free and high S-containing alloys. The C solubility in a N-free system (3, 4, 14, 24, 25, 56) is higher than that in a N-present system in this study and previous studies (12, 63). Error bars in both cases are 1−σ and, if absent, are smaller than the symbol size.

  • Fig. 2 Partition coefficients of N and C between the Fe-Ni alloy melt and the silicate melt as a function of S content in the alloy melt.

    (A) For a given P-T condition, the Embedded Image does not vary notably with an increase in S in the alloy melt. (B) In the presence of N in the alloy melt, the Embedded Image drops by an order of magnitude from S-free to high S-bearing alloys with values as low as ~10 for N-bearing, S-rich alloys. The Embedded Image in a N-free system (3, 4, 14, 24, 25, 56) is higher than that in a N-present system in this study and a previous study (12). Error bars in both cases are 1−σ and, if absent, are smaller than the symbol size.

  • Fig. 3 Ratios of the measured partition coefficients of C and N and C and S between the alloy melt and the silicate melt as a function of S content in the alloy melt.

    (A) The Embedded Image/Embedded Image ratios show that with S-free and intermediate S contents in the alloy melt, C is more siderophile than N, while for high S contents in the alloy, C is less siderophile than N. (B) The Embedded Image/Embedded Image ratios show that under S-poor conditions, C is more siderophile than S (for N-free systems), while at intermediate S (for N-bearing systems) and high S contents (for both N-free and N-bearing systems) in the alloy melt, C is less siderophile than S. Dashed horizontal lines in both panels delineate data fields where the (C/N)mantle and (C/S)mantle increase (↑) or decrease (↓) from the initial values due to equilibrium alloy-silicate fractionation. Error bars in both cases are 1−σ and, if absent, are smaller than the symbol size.

  • Fig. 4 C-N-S delivery via a giant planetary impact with proto-Earth and the results of inverse Monte Carlo simulations used to obtain the composition and the mass of the impactor.

    (A) Illustration showing the merger scenario of a volatile-bearing planetary embryo with a C-saturated, S-rich core to volatile-depleted proto-Earth. (B) The alloy/silicate ratio and the bulk S content are mutually dependent on the S content in the alloy of the impactor (the controlling variable from our experiments and calculations). (C) The bulk C content of the impactor as a function of the bulk S content as well as the alloy/silicate ratio of the impactor that yields possible volatile delivery solutions. Various chondritic meteorites are also plotted for comparison. (D) The mass of the impactor is constrained in a narrow range similar to that of Mars.

  • Fig. 5 Effect of a nonzero volatile content in the bulk silicate portion of proto-Earth on the composition and the mass of the impactor, which establishes the C-N-S budget of the present-day BSE.

    Increasing the C-N-S abundance in chondritic proportions in the silicate portion of proto-Earth (represented by circles) results in a decreasing bulk C content and mass of the impactor and an increasing S content in the impactor’s core. A decrease in the mass of the impactor is due to the delivery of a smaller fraction of the C-N-S budget of the present-day BSE by the impactor, while a superchondritic C/N ratio greater than that of the present-day BSE in the impactor necessitates a higher C enrichment in the impactor’s mantle via C exsolution from the core, which results in a higher S content of the core and lower bulk C content of the impactor. However, if the C-N-S inventory in the silicate portion of proto-Earth was affected by terrestrial core formation and atmospheric loss(es) (represented by diamonds), then, owing to the highly siderophile character of C, the bulk silicate portion of proto-Earth would be essentially C free but could retain N and S. Increasing the N-S abundance in the silicate portion of proto-Earth by up to 20% of the N-S budget of the present-day BSE results in a decreasing mass and bulk C content of the impactor, while the S content of the core almost remains constant. However, with greater than 20% of the N-S budget of the present-day BSE in silicate proto-Earth, the S content of the impactor’s core increases, delivering C/N and C/S ratios that are much greater than the C/N and C/S ratios of the BSE, and the bulk C of the impactor also increases, delivering the present-day C budget of the BSE via a proportionally smaller impactor. The star represents a C-N-S–free bulk silicate proto-Earth.

  • Fig. 6 Results of inverse Monte Carlo simulations showing the effect of the degree of equilibration of the impactor’s core with the post-merger MO on the estimated bulk C content and the mass of the impactor.

    (A) The most probable bulk C content (wt %) of the impactor as shown by the peak increases with an increasing degree of equilibration of the impactor’s core with the post-merger MO. (B) The most probable mass of the impactor with respect to the present-day Earth’s mass decreases with an increasing degree of equilibration of the impactor’s core with the post-merger MO (see Materials and Methods for details). These calculations assume the bulk silicate portion of the proto-Earth to be C-N-S free (star in Fig. 5).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/1/eaau3669/DC1

    Fig. S1. Comparison between the estimated C/N ratios of the BSE and measured C/N ratios of CI and other carbonaceous chondrites.

    Fig. S2. Backscattered electron images of typical experimental products.

    Fig. S3. Experimentally determined C solubility of the silicate melt at graphite saturation as a function of N content of the silicate melt.

    Fig. S4. Raman spectra of the experimental silicate glasses from this study showing peaks associated with C-O-N-H volatile species.

    Fig. S5. Comparison between experimentally measured C solubility in the alloy melt and the Formula and the predicted C solubility in the alloy melt and the Formula based on the parameterizations developed in this study.

    Fig. S6. Application of the experimental and parameterized alloy/silicate partition coefficients to examine whether a single-stage core formation along with an early atmospheric loss can explain the present-day abundances and ratios of C, N, and S in the BSE.

    Fig. S7. An example forward calculation to showcase the methodology used to determine the alloy/silicate ratio and the mass of the impactor for a successful inverse Monte Carlo simulation.

    Fig. S8. Effect of varying bulk C/N ratios on the composition and the mass of the impactor, which could establish the C-N-S budget of the present-day BSE.

    Fig. S9. Measured partition coefficients of S between the alloy and silicate melt as a function of S in the alloy melt.

    Fig. S10. Results of inverse Monte Carlo simulations to obtain the composition and mass of the impactor with end-member Formula values.

    Fig. S11. Results of inverse Monte Carlo simulations showing the effect of a variable Formula on the estimated bulk C content and the mass of the impactor.

    Table S1. Comparison between the estimated C/N ratios of CI and other carbonaceous chondrites with that estimated for the BSE.

    Table S2. Chemical compositions of the starting materials (in wt %).

    Table S3. Summary of the experimental conditions, quench products, oxygen fugacity, and alloy-silicate partitioning coefficients of C, N, and S.

    Table S4. Major element compositions (in wt %) of the alloy melts at 1 to 7 GPa.

    Table S5. Major element compositions (in wt %) of the silicate melts at 1 to 7 GPa.

    References (6873)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Comparison between the estimated C/N ratios of the BSE and measured C/N ratios of CI and other carbonaceous chondrites.
    • Fig. S2. Backscattered electron images of typical experimental products.
    • Fig. S3. Experimentally determined C solubility of the silicate melt at graphite saturation as a function of N content of the silicate melt.
    • Fig. S4. Raman spectra of the experimental silicate glasses from this study showing peaks associated with C-O-N-H volatile species.
    • Fig. S5. Comparison between experimentally measured C solubility in the alloy melt and the DCalloy/silicate and the predicted C solubility in the alloy melt and the DCalloy/silicate based on the parameterizations developed in this study.
    • Fig. S6. Application of the experimental and parameterized alloy/silicate partition coefficients to examine whether a single-stage core formation along with an early atmospheric loss can explain the present-day abundances and ratios of C, N, and S in the BSE.
    • Fig. S7. An example forward calculation to showcase the methodology used to determine the alloy/silicate ratio and the mass of the impactor for a successful inverse Monte Carlo simulation.
    • Fig. S8. Effect of varying bulk C/N ratios on the composition and the mass of the impactor, which could establish the C-N-S budget of the present-day BSE.
    • Fig. S9. Measured partition coefficients of S between the alloy and silicate melt as a function of S in the alloy melt.
    • Fig. S10. Results of inverse Monte Carlo simulations to obtain the composition and mass of the impactor with end-member DSalloy/silicate values.
    • Fig. S11. Results of inverse Monte Carlo simulations showing the effect of a variable DSalloy/silicate on the estimated bulk C content and the mass of the impactor.
    • Table S1. Comparison between the estimated C/N ratios of CI and other carbonaceous chondrites with that estimated for the BSE.
    • Table S2. Chemical compositions of the starting materials (in wt %).
    • Table S3. Summary of the experimental conditions, quench products, oxygen fugacity, and alloy-silicate partitioning coefficients of C, N, and S.
    • Table S4. Major element compositions (in wt %) of the alloy melts at 1 to 7 GPa.
    • Table S5. Major element compositions (in wt %) of the silicate melts at 1 to 7 GPa.
    • References (6873)

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