Earth's inner core

Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,220 km (760 mi), which is about 20% of Earth radius or 70% of the Moon's radius.

This article is about the geological center of the planet. For the geographical meaning of the term "center of the Earth", see Geographical centre of Earth.
For broader coverage of this topic, see Internal structure of Earth § Core.

There are no samples of Earth's core accessible for direct measurement, as there are for Earth's mantle. Information about Earth's core mostly comes from analysis of seismic waves and Earth's magnetic field. The inner core is believed to be composed of an iron–nickel alloy with some other elements. The temperature at the inner core's surface is estimated to be approximately 5,700 K (5,430 °C; 9,800 °F), which is about the temperature at the surface of the Sun.

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