An interesting theory recently published in the journal Science proposes that Earth may be the result of two colliding bodies that fused together early on. According to the theory, this impact created both the Earth and the 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 both modern Earth and 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.
Everything you know is a lie: Earth might actually be 2 planets smashed together | Grist