By analyzing tiny lunar zircon crystals gathered by Apollo 17 astronauts in 1972, planetary scientists recalculated the age of the Moon. Although previous assessments estimated the Moon as 4.425 billion years old, the authors discovered it is actually 4.46 billion years old — around 40 million years older than previously thought.
“These zircon crystals are the oldest known solids that formed after the giant impact,” said University of Chicago’s Professor Philipp Heck.
“And because we know how old these crystals are, they serve as an anchor for the lunar chronology.”
The sample of lunar dust used in the study was brought back by Apollo 17 astronauts in the last crewed mission to the Moon in 1972.
This dust contains tiny zircon crystals that formed billions of years ago. These crystals are a telltale sign of when the Moon must have formed.
When a Mars-size protoplanet, Theia, hit the growing proto-Earth and formed the Moon, the energy of the impact melted the rock that eventually became the lunar surface.
“When the surface was molten like that, zircon crystals couldn’t form and survive. So any crystals on the Moon’s surface must have formed after this lunar magma ocean cooled,” Professor Heck said.
“Otherwise, they would have been melted and their chemical signatures would be erased.”
Since the crystals must have formed after the magma ocean cooled, determining the age of the zircon crystals would reveal the minimum possible age of the Moon.
A previous study has suggested this age, but the new study marks the first use of an analytical method called atom probe tomography which ‘nailed down’ the age of this oldest known lunar crystal.
“In atom probe tomography, we start by sharpening a piece of the lunar sample into a very sharp tip, using a focused ion beam microscope, almost like a very fancy pencil sharpener,” said Dr. Jennika Greer, a researcher at the University of Glasgow.
“Then, we use UV lasers to evaporate atoms from…
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