Oxygen isotopic evidence for vigorous mixing during the Moon-forming   Giant Impact
  Earth and Moon are shown here to be composed of oxygen isotope reservoirs that are indistinguishable, with a difference in {\Delta}"17O of -1 +/- 5ppm (2se). Based on these data and our new planet formation simulations that include a realistic model for 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}"17O within approximately 1 per mil of the terrestrial value, suggesting that these impactors were water rich. 
Edward D. Young, Issaku E. Kohl, Paul H. Warren, David C. Rubie, Seth   A. Jacobson, Alessandro Morbidelli
astro-ph.EP