Moon over 4.5 billion years old.

The Moon's surface cooled and solidified to make its current grey and white face more than 4.5 billion years ago, say researchers who have applied new dating techniques to rocks brought back by Apollo astronauts.

This age puts the Moon's first solid rocks at about the same age Earth's first crust, bolstering the popular idea that both bodies formed crusts at about the same time and in the wake of a mega collision of a Mars-sized body with early Earth.

"For the first time we have determined the age of the Moon, which has not been done before," says German lunar researcher Dr Thorsten Kleine of the University of Munster's Institute for Mineralogy.

The results of the new work are reported in the current issue of the journal Science.

The reason it's taken so long to figure out the Moon's age is that there aren't many elements available in Moon rocks to serve as timekeepers from the time the rocks solidified.

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