It turns out the moon is older than many scientists suspected: a ripe 4.51 billion years old.
That's the newest estimate, thanks to rocks and soil collected by the Apollo 14 moonwalkers in 1971.
A research team reported Wednesday that the moon formed within 60 million years of the birth of the solar system. Previous estimates ranged within 100 million years, all the way out to 200 million years after the solar system's creation, not quite 4.6 billion years ago.
The scientists conducted uranium-lead dating on fragments of the mineral zircon extracted from Apollo 14 lunar samples. The pieces of zircon were minuscule — no bigger than a grain of sand.
The moon was created from debris knocked off from Earth, which itself is thought to be roughly 4.54 billion years old.
Apollo 14's Alan Shepard and Edgar Mitchell collected 92 pounds of rocks and used tubes to dig up soil while exploring the moon's Fra Mauro highlands in February 1971. They conducted two spacewalks, spending nine hours altogether out on the lunar surface.
It's the second major moon study this week.
The giant impact theory holds that the resulting energy formed a lunar lava ocean that later became solid. It's this solidification age that lead author Melanie Barboni of the University of California, Los Angeles and her team have now ascertained.
"We finally pinned down a minimum age for the moon formation," Barboni said.