So how DID the moon get there? Moon rocks show no evidence of the space rock supposed to have 'knocked' bits off Earth

So how DID the moon get there? Moon rocks show no evidence of the space rock supposed to have 'knocked' bits off Earth | Mail Online: "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."