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The Core: At the centre of the Earth is the core. It's upper boundary is approximately 1,800 miles (2,900 km) below the surface. The core is predominately formed of iron (85 %) and nickel (5 %) with a number of siderophile (iron liking elements forming the remainder). It is divided into two layers based on the cores state of matter, the inner core and the outer core. The inner core which is at the very centre of the Earth is a solid layer approximately 780 miles (1,250 km) thick. The core is at a very high temperature and so the outer core is always molten, however as the depth within the core increase the pressure drives the melting temperature up above the in-situ temperatures even though they reach 6700ÂºF (3700ÂºC). The outer core is approximately 1370 miles (2,200 km) thick. It is thought that the movement of the liquid outer core is responsible for the creation of earth's magnetic field. The Mantle: The mantle lies directly above the core (this boundary is known as the core-mantle-boundary or Gutenberg discontinuity and is named after the geophysicist who discovered it (trivia - Beno Gutenberg, the geophysicist in question also worked with Charles Richter in the development of the Richter magnitude scale). It's upper boundary lies approximately 6 miles (10 km) below the surface of the oceanic crust and about 19 miles(30 km) below the surface of the continental crust. The mantle is broadly divided into two main sections. The upper and the lower mantle based on changes in the crystalline structure of the mantle material caused by pressure changes at increasing depths. The mantle is approximately 1,800 miles (2,900 km) thick and makes up nearly 80 percent of the Earth's total volume. The Crust: The crust lays above the mantle and forms the upper portion of the earth's solid brittle and hard outer shell, the surface on which we are living. The crust is significantly thinner than the other layers of the earth and can be thought to float upon the denser mantle material. The Earth's crust is split into two main types, oceanic and continental crust. The main differences being in their composition which in turn effects their density and thickness. Oceanic crust is composed predominantly of mafic minerals (those with higher concentrations of the elements iron and magnesium) forming rocks such as basalt whereas the continental crust is composed mainly of felsic minerals (higher concentrations of silicon and aluminum). Continental crust tends to be less dense than oceanic crust and also of greater thickness (19 miles - 30 km thick vs 4-7 miles or 6-11 km for oceanic crust).