Why is the earth interior in most part found in a solid state despite great heat and pressure?

Core is the innermost part of the earth. It is mainly composed of nickel and iron alloy. The inner core is homogeneous in nature because it was formed by gradual cooling of the molten materials. Due to the high pressure inside the materials are compacted even though the temperature is high. It maintains to form in the solid state. By some geographical discoveries, it was said that earth's inner core is formed by a single iron crystal, because of which earth's interior is in the solid state despite heat and pressure.