New theory argues heavy elements didn’t immediately sink to Earth’s core

Science News : Gold, platinum, and other similar heavy elements are siderophile—when molten they tend to form alloys with iron. About 98% of Earth’s siderophile elements are in the iron-dominated core, and the traditional view is that they sank to the core early in Earth’s history. David Rubie of the University of Bayreuth in Germany and his colleagues are challenging that view. They argue that the bombardment of asteroids and comets that occurred during the first 100 million years of Earth’s formation kept the planet’s internal pressure and temperature high enough that siderophile elements were less likely to bond with iron. If that’s true, then the heavy elements would have remained in Earth’s mantle until they reacted with sulfur, crystallized, and fell toward the core. Rubie’s group attributes the presence of precious metals in Earth’s crust to the subsequent bombardment of asteroids, which deposited the elements on the surface.