How the Moon formed is a long-debated question. According to the giant impact theory, the Moon formed from a collision between the early Earth and a rocky body called “Theia.” Previous research believed that Earth and the Moon have identical bulk oxygen isotope compositions. For the giant impact scenario to explain this challenging constraint, it requires either early Earth and Theia to have had identical compositions or the remnants of the collision to have been extensively mixed. However, a new study from the University of New Mexico presents high-precision oxygen isotope analyses of a range of lunar lithologies and shows that Earth and the Moon, in fact, have distinctly different oxygen isotope compositions. To explain these findings, the researchers suggest that the giant collision between the early Earth and Theia only lead to to partial mixing between the bodies. The most important implication from these findings is that giant-impact models no longer have to account for the virtually indistinguishable oxygen isotopic compositions between Earth and the Moon. Lead author Erick Cano said, “I think this will open the door for an entirely new range of impact scenarios.” READ MORE