<P> The outer core of the Earth is a fluid layer about 2,400 km (1,500 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 liquid . The inner core is also referred to as the solid core . </P> <P> Seismic inversions of body waves and normal modes constrain the radius of the outer core to be 3483 km with an uncertainty of 5 km, while that of the inner core is 1220 ± 10 km . </P>

What is the term for the thick layer surrounding earth’s outer core