Bang On

In Earth by Brian Koberlein6 Comments

The dominant model for the origin of our Moon is the impact model. In this model, about 4.5 billion years ago proto-Earth was hit by a Mars-sized body known as Theia. It’s generally been thought that the collision was somewhat off-center, causing the remnants of Theia and some outer layer material from Earth to form the Moon.  But new evidence suggests the collision was more head-on

If the Earth-Moon system was caused by an off-center collision with Theia, then we would expect to see close similarities in the chemical compositions the Earth and Moon, but still some differences. Earlier research found some differences in the amount of isotopes, such as the ratio of oxygen-17 to oxygen-16 differing by about 12 parts per million between the Earth and Moon. But new work analyzing oxygen isotopes in lunar rocks and volcanic rocks on Earth found their oxygen isotopes to be indistinguishable. Since oxygen is common in both rock samples, the fact that they are indistinguishable suggests that the material forming the Earth and Moon were mixed together before they formed. This could be achieved by a more head-on collision between proto-Earth and Theia.

If that’s the case, then much of Theia became a part of Earth’s core, and our planet is actually the product of two worlds.  It’s an interesting twist on the impact origin of the Moon.

Paper: Edward D. Young, et al. Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact. Science Vol. 351, Issue 6272, pp. 493-496 (2016)


  1. 4.5 billion years ago, huh? How do they know what this object’s name was?

  2. God created the world in 7 days how did they figure the earth is billions of yes old when the first man and woman were Adam and eve and they didn’t come from frozen monkeys. The earth is only 7 thousand yrs. Old.. I would hate to think my ancestors came from a monkey with a dog face and legs like a dionasuar..what would you think.

  3. The Earths core is rotating faster than the mantel. It occurs to me that the impact with Theia might have something to do with this. Has any one done any actual research (as opposed to my wild guessing ;-} into this?

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