The moon was formed by a violent, head-on collision between the early Earth and a “planetary embryo” called Theia roughly 100 million years after the Earth formed, UCLA researchers said Thursday.
Scientists had already known about this high-speed crash, which occurred almost 4.5 billion years ago, but many thought the Earth collided with Theia at an angle of 45 degrees or more — a powerful side-swipe.
New evidence reported in Friday’s edition of the journal Science substantially strengthens the case for a head-on assault, UCLA scientists said.
The researchers analyzed seven rocks brought to the Earth from the moon by the Apollo 12, 15 and 17 missions, as well as six volcanic rocks from the Earth’s mantle — five from Hawaii and one from Arizona.
The key to reconstructing the giant impact was a chemical signature revealed in the rocks’ oxygen atoms.
In 2014, a team of German scientists reported in Science that the moon also has its own unique ratio of oxygen isotopes, different from Earth’s. The new research finds that is not the case.
“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.
Young’s research team used state-of-the-art technology and techniques to make precise and careful measurements, and verified them with UCLA’s new mass spectrometer.
“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.”
Theia, which did not survive the collision — except that it now makes up large parts of Earth and the moon — was growing and probably would have become a planet if the crash had not occurred, Young said.
Young and some other scientists believe the planet was about the same size as the Earth; others believe it was smaller, perhaps more similar in size to Mars.
— Wire reports