The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move. The inner core is a solid.
The center of the Earth is about 6,000 miles below the Earth's surface. It is a solid ball made of mostly just two metals; iron and nickel. The inner core is 800 miles thick. It is the hottest layer at about 13,000 Fahrenheit. The inner core is known for it's pressure and level of radiation.