4.5 billion years ago, when Earth was 100 million years old, Theia -- a planetary embryo around the same size as Earth -- crashed into our planet in a "violent, head-on collision" creating one single planet -- and the moon.
This crash was previously thought to be little more than a "side swipe", but new evidence from NASA-funded research out of the University Of California, Los Angeles (UCLA) reveals the collision was more of a "head-on assault" that helped shape the Earth as we know it today.
The force of the impact forced earth and Theia into one single planet -- with a piece breaking off and entering its gravitational pull to form the moon.
The research involved the study of moon rocks, comparing them to volcanic rocks from Hawaii and Arizona. The results showed there were no differences in the oxygen isotopes, and that both the lunar and volcanic rocks shared chemical signatures.
"We don’t see any difference between the Earth’s and the moon’s oxygen isotopes; they’re indistinguishable," said Edward Young, lead author of the new study and a UCLA professor of geochemistry and cosmochemistry.
"Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them. This explains why we don’t see a different signature of Theia in the moon versus the Earth."
If not for the collision, it is likely that Theia would have become a planet.
The research also raised questions about Earths origins -- including whether the collision would have removed any water contained by Earth, before asteroids rich in water hit our planet tens of millions of years later.