New research published in the journal Science proposes a stunning origin story for modern Earth: The planet we thought we knew could actually be made of two planets, which fused together 4.5 billion years ago after a collision that also formed our moon.
Astronomers have long suspected that the moon formed after a small, proto-planet, called Theia, crashed into Earth, knocking a chunk of rock into Earth’s orbit. New research by scientists at the University of California Los Angeles suggests that Theia didn’t merely sideswipe Earth, but instead fused with our planet, forming a new Earth and also the moon.
The new evidence comes from an analysis of oxygen isotopes from both volcanic rocks and lunar rocks that were brought to Earth as part of the Apollo missions. The astronomers found that the isotopes share a unique fingerprint, something that could only happen if matter from Theia and Earth thoroughly mixed together in a head-on collision. An article published on Science Alert describes the findings:
If Theia simply side-swiped Earth and produced the Moon, as previously predicted, the Moon would be made up mainly of Theia, and Earth and Moon rocks would have different oxygen isotope ratios. But this wasn’t the case.
“Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them,” said lead researcher Edward Young in a statement. “This explains why we don’t see a different signature of Theia in the Moon versus Earth.”
What this means: Theia, rather than continuing on its flight through space billions of years ago, is still here on Earth.
The study, published January 29 in the journal Science, is titled, “Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact.”