Oxygen isotope identity of the Earth and Moon with implications for the formation of the Moon and source of volatiles

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1,2,3Meike Fischer,1,4Stefan T. M. Peters,6,7Daniel Herwartz,2Paul Hartogh,1Tommaso Di Rocco,1Andreas Pack
Proceedings of the National Academy of Sciences (PNAS) 121, e2321070121 Open Access Link to Article [https://doi.org/10.1073/pnas.2321070121]
1Geowissenschaftliches Zentrum, Abteilung für Geochemie und Isotopengeologie, Georg-August-Universität Göttingen, Göttingen 37077, Germany
2Max-Planck-Institut für Sonnensystemfoschung, Abteilung Planeten und Kometen, Göttingen 37077, Germany
3Thermo Fisher Scientific (Bremen) GmbH, Bremen 28199, Germany
4Zentrum für Biodiversitätsmonitoring & Naturschutzforschung, Leibniz-Institut zur Analyse des
5Biodiversitätswandels–Standort Hamburg, Hamburg 20146, Germany
6Institut für Mineralogie und Petrologie, Universität Köln, Köln 50674, Germany
7Ruhr-Universtät Bochum, Institut für Geologie, Mineralogie und Geophysik, Bochum 44801, Germany

The Moon formed 4.5 Ga ago through a collision between proto-Earth and a planetesimal known as Theia. The compositional similarity of Earth and Moon puts tight limits on the isotopic contrast between Theia and proto-Earth, or it requires intense homogenization of Theia and proto-Earth material during and in the aftermath of the Moon-forming impact, or a combination of both. We conducted precise measurements of oxygen isotope ratios of lunar and terrestrial rocks. The absence of an isotopic difference between the Moon and Earth on the sub-ppm level, as well as the absence of isotope heterogeneity in Earth’s upper mantle and the Moon, is discussed in relation to published Moon formation scenarios and the collisional erosion of Theia’s silicate mantles prior to colliding with proto-Earth. The data provide valuable insights into the origin of volatiles in the Earth and Moon as they suggest that the water on the Earth may not have been delivered by the late veneer. The study also highlights the scientific value of samples returned by space missions, when compared to analyses of meteorite material, which may have interacted with terrestrial water.

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