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 - Beano Gutenberg, the geophysicist in question also worked with Charles Richter in the development of the Richter magnitude scale). Its 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