Earth nucleus

Why is Earth's nucleus mostly made from iron?

The iron catastrophe was a major event early in the history of Earth. After accumulation of the Earth's material into a spherical mass, the material was mostly uniform in composition. While residual heat from the collision of the material that formed the Earth was significant, heating from radioactive materials in this mass further increased the temperature until a critical condition was reached, when the material was molten enough to allow movement. At this point, the denser iron and nickel, evenly distributed throughout the mass, sank to the centre of the planet to form the core - an important process of planetary differentiation. The gravitational potential energy released by the sinking of the dense NiFe globules increased the temperature of the protoplanet above the melting point resulting in a global silicate magma which accelerated the process. This event occurred at about 500 million years into the formation of the planet.