Planetary scientists have long hypothesized that the Moon formed when an object the size of the planet Mars—known as Theia—collided with the early Earth. However, the discovery that oxygen isotope ratios on the Moon and Earth are almost identical is inconsistent to this moon-formation model that has 40 % of the Moon’s mass deriving from Theia.
A similar finding based on mass spectrometry carried out at the University of Chicago, USA, and the University of Bern, Switzerland, on the more refractory material, titanium, now suggests that the Moon was formed from material of the mantle of the proto-Earth rather than material from an enormous impactor, such as Theia.
- The proto-Earth as a significant source of lunar material,
J. Zhang, N. Dauphas, A. M. Davis, I. Leya, A. Fedkin,
Nature Geosci. 2012.