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

Abstract : 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 D 17 O. 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 D 17 O 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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https://hal.univ-brest.fr/hal-01901935
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Submitted on : Friday, January 8, 2021 - 3:21:29 PM
Last modification on : Monday, October 11, 2021 - 2:23:05 PM
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Richard Greenwood, Jean-Alix Barrat, Martin Miller, Mahesh Anand, Nicolas Dauphas, et al.. Oxygen isotopic evidence for accretion of Earth’s water before a high-energy Moon-forming giant impact. Science Advances , American Association for the Advancement of Science (AAAS), 2018, 4 (3), ⟨10.1126/sciadv.aao5928⟩. ⟨hal-01901935⟩

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