This video says about itself:
5 June 2014
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Today, a new study appeared, saying the collision between Earth and Theia was harder than thought before, and not only did parts of Theia become the moon, but also other parts became parts of planet Earth.
From Science magazine:
Rehomogenizing the Earth-Moon system
A giant impact formed the Moon, and lunar rocks provide insight into that process. Young et al. found that rocks on Earth and the Moon have identical oxygen isotopes. This suggests that well-mixed material from the giant impact must have formed both the Moon and Earth’s mantle. The finding also constrains the composition of the “late veneer”: material sprinkled onto Earth after the Moon-forming impact.
Science, this issue p. 493
Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Δ′17O 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 Δ′17O within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system.