Describe the inner and outer cores of earth. Include information about the temperature, pressure and composition.

The outer core of the Earth is a fluid layer about 2,300 km (1,400 mi) thick and composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. Its outer boundary lies 2,890 km (1,800 mi) beneath Earth's surface. The transition between the inner core and outer core is located approximately 5,150 km (3,200 mi) beneath the Earth's surface. Unlike the inner core, the outer core is not solid. This is also referred to as the "liquid core".