Mathematical models say that most of the material that formed the moon should have come from Teyi (the very object that collided with the Earth), and the smaller part from our planet. However, samples obtained by astronauts of the Apollo program show that the situation is exactly the opposite.
Purdue University researchers explain this as follows: when Theia collided with the Earth, the surface of our planet was not solid. She was covered with hot magma, which would be easier to push into space. After that, the magma hardened and turned into a moon.
Scientists note that this theory depends largely on the time of the collision. It should have happened at a very good moment in terms of temperature and magma density. The lead author of the study, Jay Melosh, also emphasizes that this assumption still does not allow for a complete agreement on all the results of observations of the Moon and the theory about it, but is an important step in this direction.