Earth’s solid inner core may be continually inching eastward relative to its liquid outer core, renewing itself by shedding its front while solidifying its back, a team of French scientists suggests. The idea counters traditional theory that the big ball at the center of the Earth stands still, growing uniformly in all directions as the planet cools. It could shed light on the nature of the core — such as its age, apparent seismic mismatches, and a mysterious coating of dense fluid on its surface.