When our planet was still forming, collisions with other planetesimals — and a Mars-sized object that sheared away the moon — turned the embryonic Earth into a roiling ball of molten rock. Iron and other heavy elements sank toward the core, and other iron-loving elements did, too. As a result, there’s plenty of gold at our planet’s center. So why, then, is there also gold in the hills? A new study supports the theory that it was all a gift from above.