A huge space rock called Theia smashed into our planet more than four billion years ago, knocking a clump of material into space, creating the moon - at least that's the theory.
There's just one problem: there's no evidence that Theia was there at all.
A new study has found no trace of Theia in rocks from the moon - leaving scientists to puzzle over how our satellite got there without a Mars-sized object slamming into the young Earth.
A giant impact between the proto-Earth and a Mars-sized object named Theia is the favoured scenario for the formation of the Moon,' says JunJun Chang of the University of Illinois at Chicago.
But if a huge object had slammed into Earth, and the moon is just the debris of that collision, traces of Theia should remain there - up to 40% of the satellite should be 'made of' Theia .... Read more at http://www.dailymail.co.uk
