Earth's Inner Core
The solid, innermost spherical core of Earth composed primarily of a crystallized iron-nickel alloy at intense pressure.
Governing formula
Radius R ≈ 1220 km, Pressure P ≈ 330–360 GPa
SI unit
GPa (Pressure) & Kelvin (~5700 K)
In depth
Discovered by Inge Lehmann in 1936. Despite temperatures matching the Sun's surface (~5700 K), extreme hydrostatic pressure (~3.5 million atmospheres) forces iron into a solid crystalline state.
Examples in the real world
PKJKP seismic wave phases confirming the inner core transmits shear S-waves.