outercore

The outer core is a liquid layer of the Earth's interior that lies between the solid inner core and the mantle. It extends from about 2,900 kilometers (roughly 1,800 miles) below the Earth's surface to about 5,150 kilometers (about 3,200 miles) beneath the surface, surrounding the solid inner core. The region is primarily composed of iron with nickel and small amounts of lighter elements such as sulfur, oxygen, silicon, or carbon. Temperatures in this layer are estimated to be around 4,000 to 6,000 degrees Celsius, and pressures range from roughly 135 to 330 gigapascals.

Because the outer core is liquid, shear (S) seismic waves cannot propagate through it, while compressional (P) waves do, though at altered velocities. Seismic data indicate a convecting, turbulent fluid that transports heat outward from the deeper interior.

The motion of the liquid iron-nickel alloy drives the geodynamo, the mechanism by which the Earth’s magnetic field is generated and sustained. Thermal and compositional buoyancy, amplified by planetary rotation, cause convection in the outer core. As the inner core slowly solidifies, light elements are released, reinforcing convective flows and maintaining magnetic field generation.

The outer core plays a crucial role in shielding the planet from solar and cosmic radiation: the generated magnetic field deflects charged particles, creating Earth's magnetosphere. Direct sampling of the outer core is not feasible with current technology; understanding relies on seismology, geomagnetic observations, high-pressure experiments on iron alloys, and numerical dynamo models.