The outer core of the Earth is a liquid layer about 2,260 km thick composed of iron and nickel which lies above the Earth's solid inner core and below its mantle. Its outer boundary lies approximately 2,890 km (1,800 mi) beneath the Earth's surface.
The earth is divided in to four layers:CRUST, MANTLE, OUTER CORE and INNER CORE. CRUST. Echo-sounding techniques are used to explore the Earth's crust. Images, similar to sonograms, are produced. A sonogram in the crust is called a seismic reflection.
Above the inner core is the outer core, a shell of liquid iron. This layer is cooler but still very hot, perhaps 7,200 to 9,000 degrees Fahrenheit (4,000 to 5,000 degrees Celsius). It too is composed mostly of iron, plus substantial amounts of sulfur and nickel.