<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> <P> Estimates for the temperature of the outer core are about 3,000--4,500 K (2,730--4,230 ° C; 4,940--7,640 ° F) in its outer regions and 4,000--8,000 K (3,730--7,730 ° C; 6,740--13,940 ° F) near the inner core . Evidence for a fluid outer core includes from seismology which shows that seismic shear - waves are not transmitted through the outer core Because of its high temperature, modeling work has shown that the outer core is a low viscosity fluid that convects turbulently . Eddy currents in the nickel iron fluid of the outer core are believed to influence the Earth's magnetic field . The average magnetic field strength in the Earth's outer core was measured to be 2.5 millitesla, 50 times stronger than the magnetic field at the surface . The outer core is not under enough pressure to be solid, so it is liquid even though it has a composition similar to the inner core . Sulfur and oxygen could be present in the outer core . </P> <P> As heat is transferred outward toward the mantle, the net trend is for the inner boundary of the liquid region to freeze, causing the solid inner core to grow . This growth rate is estimated to be 1 mm per year . </P>

Facts on the outer core of the earth