The Inner Core

The Inner Core is one of five sections of the Earth's Core that is the centre part.It was discovered in 1936
by seismologist Inge Lehmann.

It is thought to consist of iron-nickel alloy and may have a temperature similar to that of the Sun's surface, approximately 5430 C (5700 K).  It is surrounded by thick layers of outer core, mantle, upper mantle and crust.

A man named J.A Jacobs was the first person to have a theory of the fact that the inner core was freezing and growing out of liquid outer core due to the gradual cooling of Earth's interior, which is about 100 degrees Celsius per billion years. It's innermost hottest part as detected by seismological studies, is a primarily solid ball approximately 1,220 km in radius or 70% of that of the moon.

The outer core is surrounded by a thick layer of mantle, which in some places under the ocean is actually exposed on the surface of the Earth.