Oxygen isotopic evidence for accretion of Earth's water before a high-energy Moon-forming giant impact

Type Article
Date 2018-03
Language English
Author(s) Greenwood Richard C.1, Barrat Jean-AlixORCID2, Miller Martin F.1, 3, Anand MaheshORCID1, 4, Dauphas Nicolas5, 6, Franchi Ian A.1, Sillard Patrick7, Starkey Natalie A.1
Affiliation(s) 1 : Open Univ, Sch Phys Sci, Planetary & Space Sci, Walton Hall, Milton Keynes MK7 6AA, Bucks, England.
2 : Univ Bretagne Occidentale, Inst Univ Europeen Mer, Lab Geosci Ocean, CNRS,UMR 6538, Plouzane, France.
3 : British Antarctic Survey, Madingley Rd, Cambridge CB3 0ET, England.
4 : Nat Hist Museum, Dept Mineral, Cromwell Rd, London SW7 5BD, England.
5 : Univ Chicago, Dept Geophys Sci, Origins Lab, 5734 South Ellis Ave, Chicago, IL 60637 USA.
6 : Univ Chicago, Enrico Fermi Inst, 5734 South Ellis Ave, Chicago, IL 60637 USA.
7 : Ctr Rech Econ & Stat, 5 Ave Henry Le Chatelier, F-91120 Palaiseau, France.
Source Science Advances (2375-2548) (Amer Assoc Advancement Science), 2018-03 , Vol. 4 , N. 3 , P. eaao5928 (9p.)
DOI 10.1126/sciadv.aao5928
WOS© Times Cited 67
Note Correction for the Research Article: “Oxygen isotopic evidence for accretion of Earth’s water before a high-energy Moon-forming giant impact” by R. C. Greenwood, J. Barrat, M. F. Miller, M. Anand, N. Dauphas, I. A. Franchi, P. Sillard and N. A. Starkey In the article “Oxygen isotopic evidence for accretion of Earth’s water before a high-energy Moon-forming giant impact,” in the first paragraph of the Results section, the final term in the definition of Δ17O was corrected from “+ γ” to “– γ”. In paragraph 5 of the Discussion section, the CI value, originally published as −1.03, was corrected to −0.24. The relevant sentence now correctly reads, “Compared to terrestrial samples, which have an average ɛ100 Ru value of +0.05, CIs have a value of −0.24 and ordinary chondrites have an average value of −0.29 (31).” The HTML and PDF versions of the paper have been corrected.

The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples. We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Delta O-17. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Delta O-17 values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post-giant impact additions to Earth. On the basis of this assumption, our data indicate that post-giant impact additions to Earth could have contributed between 5 and 30% of Earth's water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth's water was accreted before the giant impact and not later, as often proposed.

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Greenwood Richard C., Barrat Jean-Alix, Miller Martin F., Anand Mahesh, Dauphas Nicolas, Franchi Ian A., Sillard Patrick, Starkey Natalie A. (2018). Oxygen isotopic evidence for accretion of Earth's water before a high-energy Moon-forming giant impact. Science Advances, 4(3), eaao5928 (9p.). Publisher's official version : https://doi.org/10.1126/sciadv.aao5928 , Open Access version : https://archimer.ifremer.fr/doc/00638/74995/