Scientists cannot put the Moon on a scale and read its birthday. They date minerals that formed during its earliest history, then use those ages to constrain when the Moon must already have existed and cooled enough to make crust.
The Moon likely formed near the beginning of the solar system
NASA describes the leading model as a giant collision involving the young Earth roughly 4.5 billion years ago. Debris from that event coalesced into the Moon, which was initially hot and largely molten.
The crystal cannot predate the crust that produced it
Zircon is valuable because uranium atoms enter the crystal when it forms while lead is largely excluded. Over time, uranium decays to lead at known rates, creating a radiometric clock.
A tiny crystal returned in 1972 became the key sample
Researchers reexamined zircon from Apollo 17 sample 72255 using atom-probe tomography. The work supported a uranium-lead crystallization age of about 4.46 billion years.
The Moon had to exist before the crystal could form
The giant impact, magma ocean and cooling all had to occur before zircon crystallized. The 4.46-billion-year date therefore pushes the minimum formation age of the Moon farther back—it does not prove the impact happened at the exact same moment.
New samples can refine the chronology again
NASA continues to identify the age difference between lunar crust and mantle materials as an important research target. Future samples from unexplored regions can test whether the Apollo record represents the Moon’s earliest global history.
A 50-year-old Apollo sample is still changing the Moon’s timeline
The remarkable part is not just the number. It is that a crystal smaller than a grain of sand can preserve a clock from the first tens of millions of years of the Earth-Moon system.