Many, many moons ago, a proto-planet the size of Mars slammed into early Earth. In its wake, the collision left a planetary disk that formed the moon and sent bits of proto-planet flying into our solar system’s main asteroid belt. The collision occurred around 4.47 billion years ago, researchers report in the April 17 Science. That closely matches previous estimates of the moon’s age.
While the finding might not be Earth-shattering, the methods are new. The team looked at previously dated meteorites that had evidence of explosive heating and ancient argon, and they modeled the collision and its blowback on the asteroid belt to pinpoint the timing of the planetary crash.