Our planet Earth is made up of three main layers; starting at the outside and working in, they are called the crust, mantle and core. The crust, including the land and oceans, is part of the biosphere upon which all known life depends. The mantle forms the next layer, and the core lies at the center. The core itself has two distinct layers, simply referred to as the outer core and inner core. The inner core is by far the hottest and densest part of the Earth.
Solid Inner Core
It’s a common misconception that the Earth’s inner core is liquid; only the outer core is in a liquid state. The inner core forms a solid mass because of the tremendous pressure exerted by the other layers pressing down on it.
Location and Size
The inner core lies about 3,500 miles beneath the surface of the crust – roughly the distance from New York to Los Angeles. The inner core’s diameter is roughly 1,500 miles.
Most of the Earth’s inner core consists of iron; scientists speculate that it may also contain several other elements, including carbon, sulfur, potassium and silicon.
The inner core reaches an estimated 10,000 degrees Fahrenheit -- a temperature hotter than the surface of the Sun. Although the main constituent, iron, boils at a “mere” 5,000 degrees Fahrenheit, the gigantic pressures present at the center of the Earth force the core into a solid state.
Combined, the inner and outer cores produce the magnetic field that surrounds the Earth. As the Earth spins on its axis, the core rotates. The movement of the liquid outer core around the mostly-solid inner core creates the magnetic field due to a physical process called the dynamo effect.