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Deep-mantle krypton reveals Earth’s early accretion of carbonaceous matter

Nature volume 600, pages 462–467 (2021)Cite this article

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Abstract

Establishing when, and from where, carbon, nitrogen and water were delivered to Earth is a fundamental objective in understanding the origin of habitable planets such as Earth. Yet, volatile delivery to Earth remains controversial1,2,3,4,5. Krypton isotopes provide insights on volatile delivery owing to their substantial isotopic variations among sources6,7,8,9,10, although pervasive atmospheric contamination has hampered analytical efforts. Here we present the full suite of krypton isotopes from the deep mantle of the Galápagos and Iceland plumes, which have the most primitive helium, neon and tungsten isotopic compositions11,12,13,14,15,16. Except for 86Kr, the krypton isotopic compositions are similar to a mixture of chondritic and atmospheric krypton. These results suggest early accretion of carbonaceous material by proto-Earth and rule out any combination of hydrodynamic loss with outgassing of the deep or shallow mantle to explain atmospheric noble gases. Unexpectedly, the deep-mantle sources have a deficit in the neutron-rich 86Kr relative to the average composition of carbonaceous meteorites, which suggests a nucleosynthetic anomaly. Although the relative depletion of neutron-rich isotopes on Earth compared with carbonaceous meteorites has been documented for a range of refractory elements1,17,18, our observations suggest such a depletion for a volatile element. This finding indicates that accretion of volatile and refractory elements occurred simultaneously, with krypton recording concomitant accretion of non-solar volatiles from more than one type of material, possibly including outer Solar System planetesimals.

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Fig. 1: Krypton isotopic patterns of Galápagos and Iceland samples.
Fig. 2: Krypton isotopic compositions of Galápagos and Iceland samples.
Fig. 3: Xenon isotope composition of Galápagos and Iceland samples.
Fig. 4: Mixing proportions in the plume sources.
Fig. 5: Estimated 86Kr/84Kr ratio based on different mixing scenarios.

Data availability

The geochemical data that support the findings of this study are archived on EarthChem at https://ecl.earthchem.org/view.php?id=2065. Source data are provided with this paper.

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Acknowledgements

We thank M. Huh for assistance in the lab; and M. Huyskens, S. Stewart and S. J. Lock for helpful discussions and comments on the manuscript. The He isotope analyses in the OSU noble gas lab were supported by NSF 1763255. The collection of the Fernandina samples and WHOI participation was supported by NSF Ocean Sciences.

Author information

Authors and Affiliations

  1. Department of Earth and Planetary Sciences, University of California, Davis, Davis, CA, USA

    Sandrine Péron & Sujoy Mukhopadhyay

  2. Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

    Mark D. Kurz

  3. College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA

    David W. Graham

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  1. Sandrine Péron
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Contributions

S.P. and S.M. designed the study. S.P. carried out the noble gas (Ne, Ar, Kr and Xe) analyses, interpreted the data and wrote the manuscript with feedback from S.M. M.D.K. and D.W.G. provided the samples, discussed the results and contributed to the final manuscript preparation. D.W.G. carried out the He and CO2 analyses of sample DG2017.

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Correspondence to Sandrine Péron.

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Extended data figures and tables

Extended Data Fig. 1 Krypton isotopic patterns for each analysis.

Isotopic ratios are in delta notation δiKr = ((iKr/84Kr)sample/(iKr/84Kr)air − 1) × 103. a, Sample D22B-1. b, Sample D22B-2. c, Sample D22B-3. d, Sample D22A. e, Samples DG2017-1 and DG2017-2. Patterns of solar wind24, AVCC and Phase Q25 are shown for reference.

Source data

Extended Data Fig. 2 Krypton–neon isotope plot.

The krypton isotopic compositions of the Galápagos and Iceland mantle sources are not precisely known; our data represent a lower limit as explained in Methods. As such, a range is indicated for the deep mantle spanning the Phase Q and AVCC Kr isotopic compositions. The mixing hyperbolae show that accumulating crushing steps with 20Ne/22Ne ratios >11.75 allow to obtain Kr isotopic ratios close to the mantle source ratios.

Source data

Extended Data Fig. 3 Estimation of the probability of the observed deficit in 86Kr for the D22 (Galápagos) and DG2017 (Iceland) samples.

The black rectangle represents the probability (0.01%) that both measured 86Kr/84Kr ratios for the Galápagos and Iceland plume sources are higher than the predicted values (Fig. 5). The white rectangle represents the probability that both measured ratios are lower than the predicted values, the blue rectangle that the measured ratio for the Galápagos source is lower than the predicted value with the measured ratio for Iceland being higher than the predicted value, and the green rectangle that the measured ratio for the Iceland source is lower than the predicted value with the measured ratio for Galápagos being higher than the predicted value. There is a 99.9% probability that Earth’s deep mantle has a deficit in 86Kr relative to AVCC.

Extended Data Fig. 4 Reproducibility of the air standard for krypton isotopic ratios.

a, 78Kr/84Kr. b, 80Kr/84Kr. c, 82Kr/84Kr. d, 83Kr/84Kr. e, 86Kr/84Kr. This set of standards was measured over 13 days and include three sizes of air standard, ranging from 7.52 × 10−12 cc to 2.37 × 10−11 cc of 84Kr. For the samples, only one size of the air standard was used (84Kr of 2.37 × 10−11 cc), measurements of this air standard size show an even better reproducibility (typically of 2‰ for 78Kr/84Kr, of 2.5‰ for 80Kr/84Kr, of 1‰ for 82Kr/84Kr, of 1.5‰ for 83Kr/84Kr and of 1‰ for 86Kr/84Kr).

Extended Data Fig. 5 Three-neon isotope plot for the step-crushing analyses and argon–neon isotope plot for the accumulated gas.

a, Neon isotopic ratios for samples D22B-1, D22B-2, D22B-3 and D22A (Galápagos), compared with literature data11. b, Neon isotopic ratios for samples DG2017-1 and DG2017-2 (Iceland), compared with literature data14,15,54. Supplementary Table 2 indicates for which step heavy noble gases were accumulated. Neon-B4, Sun83, solar wind84. c, 40Ar/36Ar versus 20Ne/22Ne for samples D22B-1, D22B-2, D22B-3 and D22A (Galápagos), compared with literature data11. d, 40Ar/36Ar versus 20Ne/22Ne for samples DG2017-1 and DG2017-2 (Iceland) compared with literature data14,15,54. The 20Ne/22Ne ratios for samples D22B-1, D22B-2, D22B-3, D22A, DG2017-1 and DG2017-2 are the average ratios of the accumulated steps, refer to Supplementary Table 2. The measured 40Ar/36Ar ratios as well as the average 20Ne/22Ne ratios are consistent with previous measurements for these same samples.

Source data

Extended Data Table 1 Krypton isotopic compositions of samples AHA-NEMO2-D22A and AHA-NEMO2-D22B (hereafter D22A and D22B, Fernandina, Galápagos, respectively) and DG2017 (Midfell, Iceland)
Full size table
Extended Data Table 2 Xenon abundances and isotopic ratios measured with the accumulation protocol for the Galápagos (AHA-NEMO2-D22A and AHA-NEMO2-D22B) and Iceland (DG2017) samples
Full size table
Extended Data Table 3 Compilation of carbonaceous, ordinary and enstatite chondrites krypton isotopic data67,68,69,70,80,81,82
Full size table
Extended Data Table 4 Argon abundances and isotopic ratios measured with the accumulation protocol for the Galápagos (AHA-NEMO2-D22A and AHA-NEMO2-D22B) and Iceland (DG2017) samples
Full size table
Extended Data Table 5 Results of the accumulation tests with air standard aliquots of 7.52 × 10−12 cc of 84Kr
Full size table

Supplementary information

Supplementary Tables

This file contains Supplementary Tables 1 and 2.

Source data

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Péron, S., Mukhopadhyay, S., Kurz, M.D. et al. Deep-mantle krypton reveals Earth’s early accretion of carbonaceous matter. Nature 600, 462–467 (2021). https://doi.org/10.1038/s41586-021-04092-z

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  • DOI: https://doi.org/10.1038/s41586-021-04092-z

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