<P> The crust ranges from 5 -- 70 kilometres ( 3.1 -- 43.5 mi ) in depth and is the outermost layer . The thin parts are the oceanic crust , which underlie the ocean basins ( 5 -- 10 km ) and are composed of dense ( mafic ) iron magnesium silicate igneous rocks , like basalt . The thicker crust is continental crust , which is less dense and composed of ( felsic ) sodium potassium aluminium silicate rocks , like granite . The rocks of the crust fall into two major categories -- sial and sima ( Suess , 1831 -- 1914 ) . It is estimated that sima starts about 11 km below the Conrad discontinuity ( a second order discontinuity ) . The uppermost mantle together with the crust constitutes the lithosphere . The crust - mantle boundary occurs as two physically different events . First , there is a discontinuity in the seismic velocity , which is most commonly known as the Mohorovičić discontinuity or Moho . The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar ( above ) to rocks that contain no feldspars ( below ) . Second , in oceanic crust , there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites , which has been observed from deep parts of the oceanic crust that have been obducted onto the continental crust and preserved as ophiolite sequences . </P>
<P> The crust ranges from 5 -- 70 kilometres ( 3.1 -- 43.5 mi ) in depth and is the outermost layer . The thin parts are the oceanic crust , which underlie the ocean basins ( 5 -- 10 km ) and are composed of dense ( mafic ) iron magnesium silicate igneous rocks , like basalt . The thicker crust is continental crust , which is less dense and composed of ( felsic ) sodium potassium aluminium silicate rocks , like granite . The rocks of the crust fall into two major categories -- sial and sima ( Suess , 1831 -- 1914 ) . It is estimated that sima starts about 11 km below the Conrad discontinuity ( a second order discontinuity ) . The uppermost mantle together with the crust constitutes the lithosphere . The crust - mantle boundary occurs as two physically different events . First , there is a discontinuity in the seismic velocity , which is most commonly known as the Mohorovičić discontinuity or Moho . The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar ( above ) to rocks that contain no feldspars ( below ) . Second , in oceanic crust , there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites , which has been observed from deep parts of the oceanic crust that have been obducted onto the continental crust and preserved as ophiolite sequences . </P>
what is the solid outer layer of the earth called
what is the solid outer layer of the earth called
The crust
The crust