About 4.5 billion years ago, a “planetary embryo” called Theia collided head-on with Earth, according to new research.
The collision not only created Earth as we know it today but also formed the moon, UCLA geochemists reported on Jan. 28.
While scientists already knew about the crash, they believed it occurred at a 45-degree angle. But it turns out the collision was direct -- and violent.
In order to arrive at this conclusion, researchers compared the chemical composition of moon rocks with volcanic rocks from Hawaii and Arizona.
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“We don’t see any difference between the Earth’s and the moon’s oxygen isotopes; they’re indistinguishable,” said lead author Edward Young, a professor of geochemistry and cosmochemistry at UCLA.
If Earth and Theia had collided at an angle, Earth and the moon would have different oxygen isotopes.
Scientists believe that Theia was similar in size to either Mars or Earth. While it did not survive the collision, remnants survive on both Earth and the moon.
"Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them," Young said. "This explains why we don't see a different signature of Theia in the moon versus the Earth."