Our study of the oxygen isotope composition of the Earth and Moon has just been published in Science Advances
It is Open Access so you can download the full paper here: Greenwood et al. 2018
There is a short summary article on the Open University website:
Oxygen isotopic evidence for accretion of Earth’s water prior to a high energy Moon-forming giant impact
Richard C. Greenwood, Jean-Alix Barrat, Martin F. Miller, Mahesh Anand, Nicolas Dauphas, Ian A. Franchi, Patrick Sillard, Natalie A. Starkey
The Earth-Moon system likely formed by collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and 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 Δ17O. Taking aubrite meteorites as candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between target and impactor. Alternatively, the degree of similarity between the Δ17O values of the impactor and proto-Earth must have been significantly closer than that between the 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 the Earth. On the basis of this assumption, our data indicates that post-giant impact additions to the Earth could have contributed between 5 and 30 % of Earth’s water, depending on global water estimates. Consequently, our data indicate that the main fraction of Earth’s water was accreted before the giant impact and not later, as often proposed.