The moon is 4.36 billion years old, up to 200 million years younger than thought, according to the analysis of lunar rocks.
The estimate, reported in Thursday's issue of Nature, comes from a new dating of isotopes of lead and neodymium found in samples of ferroan anorthosite, a crustal rock that derives from magma.
A common theory for the origin of the moon is that it was created by an impact between a large planet-sized object and the nascent Earth.
The molten material, or magma, that was ejected from this giant collision progressively cooled, hardening into Earth's rocky, barren and airless satellite.
'The extraordinarily young age of this lunar sample either means that the moon solidified significantly later than previous estimates, or that we need to change our entire understanding of the moon's geochemical history,' said Richard Carlson of the Carnegie Institution for Science in Washington.
If the estimate is right, it implies that the oldest crusts on both Earth and moon formed at roughly the same time, both of them shortly after the big smashup.
The dating concurs with a similar age estimate for zircons found in Western Australia that are the oldest terrestrial minerals found.
