Based on the abundance of chemical elements in the solar system, the theory of planetary formation, and other chemical constraints regarding the remainder of Earth's volume, the inner core is composed primarily of a nickel–iron alloy referred to as Nife: 'Ni' for nickel, and 'Fe' for ferrum or iron. Because the inner core is more dense (12.8 ~ 13.1)g⁄cm³ than pure iron or nickel, even under heavy pressures, it's believed that the remaining part of the core is composed of gold, platinum and other siderophile elements in quantity enough to coat Earth's surface for 0.45 m (1.5 feet). The relative abundance of precious metals and other heavy elements respect to Earth's crust is explained with the theory of iron catastrophe, an event occured before the first eon during the accretion of early Earth.
The temperature of the inner core can be estimated using experimental and theoretical constraints on the melting temperature of impure iron at the pressure (about 330 GPa) of the inner core boundary, yielding estimates of 5,700 K (5,430 °C; 9,800 °F). The range of pressure in Earth's inner core is about 330 to 360 gigapascals (3,300,000 to 3,600,000 atm), and iron can only be solid at such high temperatures because its melting temperature increases dramatically at these high pressures (see the Clausius–Clapeyron relation).