The Earth and Moon share a past etched in silicon, and it hints that the favoured theory of how the Moon formed isn't quite right.
Most astronomers believe that the Moon formed when a Mars-sized object struck Earth. If this is the case, the Moon should contain mainly rock from the impacting body. However, Alex Halliday of the University of Oxford and his colleagues have evidence suggesting that this isn't so.
More: http://space.newscientist.com/article.ns?id=mg19426104.900&feedId=space_rss20