The Earth's inner core is solid. It is primarily composed of an iron-nickel alloy, with some lighter elements possibly present. Despite its extremely high temperature-estimated around 5,200 to 6,000 °C (about 9,400 to 10,800 °F), which is higher than the melting point of iron at surface pressure-the inner core remains solid because of the immense pressure exerted on it from the overlying layers of the Earth. This pressure, estimated to be about 3.6 million atmospheres, prevents the iron and nickel from melting, keeping the inner core in a solid phase
. Seismic wave studies, which analyze how waves travel through the Earth, have been crucial in determining the solid state of the inner core, as seismic waves behave differently when passing through solids versus liquids. The boundary between the solid inner core and the liquid outer core is marked by a seismic discontinuity known as the Lehman Discontinuity
. In summary:
- State: Solid
- Composition: Mainly iron and nickel alloy, with some lighter elements
- Temperature: Approximately 5,200–6,000 °C
- Reason for solidity: Extremely high pressure prevents melting despite high temperature
- Evidence: Seismic wave behavior and geophysical studies
This solid state under extreme conditions is consistent with the Simon-Glatzel equation, which relates melting points to pressure and temperature
