It’s a big claim, but scientists say they have discovered evidence that the Moon was born in a flaming blaze of glory when a body the size of Mars collided with the early Earth. The evidence might not seem all that impressive to a nonscientist: a tiny excess of a heavier variant of the element zinc in Moon rocks. But the enrichment probably arose because heavier zinc atoms condensed out of the roiling cloud of vaporized rock created by a catastrophic collision faster than lighter zinc atoms, and the remaining vapor escaped before it could condense.