THE EVIDENCE: A LUMP OF MOON ROCK
The research team – led by Paul Warren (left), Edward Young (centre) and Issaku Kohl (right) of the University of California in Los Angeles – examined rock samples brought back from the moon by the Apollo 12, 15 and 17 missions. When they compared them to samples from Earth, they found the oxygen content was almost identical. This provided the researchers with evidence that Earth and the moon are made of the same material – meaning Theia must have merged with our planet. If Theia had just sideswiped Earth, the moon would have a different chemical fingerprint.