Earth’s innermost layer is a 400-mile-wide ball of iron, new study suggests

Scientists have long wondered what lies at the very center of the Earth, and the latest research is putting weight behind a theory that our planet has a distinct ball of iron within its metallic core.

Beneath the outermost crust, the mantle and the molten-liquid outer core lies the Earth’s solid metal center — which actually has a hidden layer, or an “innermost inner core” within, according to a new study published Tuesday in the journal Nature Communications.

The monumental finding suggests the Earth has five major layers instead of four, and offered new details scientists could use to help unlock some of the oldest mysteries about our planet and how it was formed.