The center of the Earth is called the inner core. It is indeed composed primarily of iron and nickel, with a small amount of other elements like sulfur, silicon, and oxygen.

Here's a breakdown of the Earth's structure and the inner core:

* Crust: The thin, outermost layer of the Earth.

* Mantle: The thickest layer, composed of mostly solid rock.

* Outer Core: A liquid layer of iron and nickel.

* Inner Core: A solid sphere of iron and nickel.

The inner core is under immense pressure from the weight of the Earth above it. This pressure is so great that it forces the iron and nickel atoms to pack tightly together, making it solid despite the extremely high temperature (around 5,200°C or 9,392°F).

Let me know if you have more questions!