Which layer of the Earth is primarily composed of solid iron and nickel?

The layer of the Earth primarily composed of solid iron and nickel is the inner core. The inner core is located at the very center of the Earth and is characterized by extremely high pressures and temperatures, which cause the iron and nickel to exist in a solid state despite the high temperatures. The inner core is about 1,500 miles (2,400 kilometers) thick, and its solid state is a result of the immense pressure that prevents the iron and nickel from melting.

In contrast, the outer core, while also composed of iron and nickel, is in a liquid state due to the lower pressures at that depth. The crust and mantle are made up of different minerals and elements; the crust consists mainly of silicate rocks and minerals, while the mantle is composed of silicate minerals that are rich in magnesium and iron but are not solely made up of iron and nickel. The distinctions between these layers are significant in understanding the Earth's composition and behavior.