This is the best summary I could come up with:

Billions of years ago, a huge object the size of Mars collided with the Earth, scientists believe.

The discovery was made using dust that had been bought back from the Moon by astronauts who travelled there in the Apollo 17 mission in 1972.

“These samples were brought to Earth half-a-century ago, but only today do we have the necessary tools to perform microanalysis at the requisite level, including atom-probe tomography.”

Researchers analysed the crystals on an atomic basis, allowing them to count how many of them had seen radioactive decay.

“Radiometric dating works a little bit like an hourglass,” said the Field Museum’s Philipp Heck, the study’s senior author.

An article describing the work, ‘4.46 Ga zircons anchor chronology of lunar magma ocean’, is published in the journal Geochemical Perspectives Letters.

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