Scientists know that the Earth's outer core is liquid because seismic shear waves (S-waves) are not transmitted through it
. S-waves can only travel through solids, so their inability to penetrate the outer core indicates it is liquid
. Density and the Earth's magnetic field also suggest that the outer core is liquid
. The outer core is a fluid layer composed mostly of iron and nickel that lies above the solid inner core and below the mantle
. It is approximately 2,260 km (1,400 mi) thick and is located about 2,889 km (1,795 mi) beneath the Earth's surface
