At the center of the planet lies a sphere of metal. Earth’s core is composed mainly of iron and nickel and consists of a solid inner core surrounded by a liquid outer core. Pressures are millions of times atmospheric and temperatures reach several thousand degrees.

The liquid outer core convects vigorously, generating Earth’s magnetic field through the geodynamo process. Seismic waves change speed and direction at the core-mantle boundary, allowing geophysicists to map its structure. The inner core grows slowly as the Earth cools and more iron solidifies.

Without the core’s magnetic field, the surface would be exposed to far more solar wind and cosmic radiation. Heat escaping from the core also helps drive mantle convection. Indirect evidence from seismology, mineral physics, and the magnetic field remains the primary means of studying this inaccessible region.

• Central metallic region of Earth
• Solid inner core and liquid outer core
• Generates the magnetic field
• Studied mainly through seismic waves