Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact

Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Delta'O-17 of -1 +/- 5 parts per million (2 standard error). On the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. The results indicate that the late veneer impactors had an average Delta'O-17 within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system.