KRDOBy Jackie Wattles, CNN 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…