A late arrival for platinum and gold?

For decades, geologists have wondered why Earth’s mantle, between the planet’s crust and core, contains as much platinum, gold, and certain other elements as it does. New research suggests that this mysterious overabundance may be due to alien invasions.

These substances are siderophilic, or iron-loving. During Earth’s early formation, they should have been much more attracted to the planet’s iron core than to its mantle, which is dominated by silicates.