The primary substance that makes up the Earth's core is primarily iron, combined with smaller amounts of nickel and other elements like sulfur and oxygen. The core is divided into two layers: the solid inner core and the liquid outer core. The inner core, with temperatures similar to the surface of the Sun, is thought to be solid despite the high heat due to immense pressure. The movement of the molten outer core around the solid inner core is vital for generating the Earth's magnetic field.