In 1972, Apollo 17 astronauts carried home a stash of Moon rocks that more than 50 years later are still delivering new scientific insights. Turns out that one of the bits recently analyzed suggests that the Moon is 40 million years older than we thought. Evidence suggests that the Moon was formed when an object the size of Mars smashed into the Earth, blasting a big hunk of our planet into orbit. But when did that actually happen? This new finding pinpoints it at around 108 million years after the formation of our solar system.
To arrive at their conclusions, scientists studied speckles of a mineral called "zircon," present in moon samples brought to Earth in 1972 by the final Apollo mission. Originally formed when the moon's impact-driven molten surface solidified after the collision that led to its birth, scientists believe zircon crystals are the first solids to have crystallized after the moon's formation. Therefore, they could exhibit tell-tale signs of the moon's age.
"Because we know how old these crystals are, they serve as an anchor for the lunar chronology," said [University of Chicago geophysicist Philipp] Heck.