The moon is about as old as we thought it was

Meteorite from Chelyabinsk, Russia

Meteorites with dark veins and blobs, like the sample above, experienced high heat when the blast from the planetary collision that formed the moon hit the asteroid belt 4.47 billion years ago. The dark coloration on the edge of the sample is from entering the Earth's atmosphere.

Qingzhu Yin, University of California, Davis

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.

A simulation of the crash that likely formed the moon depicts a Mars-sized proto-planet colliding with proto-Earth. Particles depicted in red were flung beyond the area around Earth to the main asteroid belt and beyond. Yellow and green particles eventually became part of the moon, while blue particles got mixed into early Earth. Robin Canup, Southwest Research Institute

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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