"If you want to date this process, we use the mineral zircon, because that's the best time capsule you can find," she said.
The researchers studied zircon fragments in rocks collected by Apollo 14 astronauts in 1971. The team dated the samples radiometrically, by measuring how much of their uranium had decayed into lead, and how their hafnium had decayed into various "daughter isotopes." (Isotopes are variants of an element that have the same number of protons in their nuclei but different numbers of neutrons.)
The team's analyses show that the zircon fragments are pristine and ancient, dating back to the solidification of the magma ocean, Barboni said. The researchers also managed to correct for the influence of galactic cosmic-ray impacts, which can complicate dating attempts by injecting neutrons into samples, she added.
The age the team came up with for the moon — 4.51 billion years, give or take 10 million years — should therefore stand the test of time, Barboni said.
How Old Is the #Moon? Scientists Say They Finally Know https://t.co/QiNiDnY5oI pic.twitter.com/Mi90mgi7xM
— SPACE.com (@SPACEdotcom) 12 January 2017
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