<P> The core -- mantle boundary ( CMB in the parlance of solid earth geophysicists ) of the Earth lies between the planet 's silicate mantle and its liquid iron - nickel outer core . This boundary is located at approximately 2891 km ( 1796 mi ) depth beneath the Earth 's surface . The boundary is observed via the discontinuity in seismic wave velocities at that depth . This discontinuity is due to the differences between the acoustic impedances of the solid mantle and the molten outer core . P - wave velocities are much slower in the outer core than in the deep mantle while S - waves do not exist at all in the liquid portion of the core . Recent evidence suggests a distinct boundary layer directly above the CMB possibly made of a novel phase of the basic perovskite mineralogy of the deep mantle named post-perovskite . Seismic tomography studies have shown significant irregularities within the boundary zone and appear to be dominated by the African and Pacific large low - shear - velocity provinces ( LLSVPs ) . The ~ 200 km thick layer of the lower mantle directly above the boundary is referred to as the D '' ( `` D double - prime '' or `` D prime prime '' ) and is sometimes included in discussions regarding the core -- mantle boundary zone . The D '' name originates from the mathematician Keith Bullen 's designations for the Earth 's layers . His system was to label each layer alphabetically , A through G , with the crust as ' A ' and the inner core as ' G ' . In his 1942 publication of his model , the entire lower mantle was the D layer . In 1950 , Bullen found his ' D ' layer to actually be two different layers . The upper part of the D layer , about 1800 km thick , was renamed D ′ ( D prime ) and the lower part ( the bottom 200 km ) was named D '' . </P>
<P> The core -- mantle boundary ( CMB in the parlance of solid earth geophysicists ) of the Earth lies between the planet 's silicate mantle and its liquid iron - nickel outer core . This boundary is located at approximately 2891 km ( 1796 mi ) depth beneath the Earth 's surface . The boundary is observed via the discontinuity in seismic wave velocities at that depth . This discontinuity is due to the differences between the acoustic impedances of the solid mantle and the molten outer core . P - wave velocities are much slower in the outer core than in the deep mantle while S - waves do not exist at all in the liquid portion of the core . Recent evidence suggests a distinct boundary layer directly above the CMB possibly made of a novel phase of the basic perovskite mineralogy of the deep mantle named post-perovskite . Seismic tomography studies have shown significant irregularities within the boundary zone and appear to be dominated by the African and Pacific large low - shear - velocity provinces ( LLSVPs ) . The ~ 200 km thick layer of the lower mantle directly above the boundary is referred to as the D '' ( `` D double - prime '' or `` D prime prime '' ) and is sometimes included in discussions regarding the core -- mantle boundary zone . The D '' name originates from the mathematician Keith Bullen 's designations for the Earth 's layers . His system was to label each layer alphabetically , A through G , with the crust as ' A ' and the inner core as ' G ' . In his 1942 publication of his model , the entire lower mantle was the D layer . In 1950 , Bullen found his ' D ' layer to actually be two different layers . The upper part of the D layer , about 1800 km thick , was renamed D ′ ( D prime ) and the lower part ( the bottom 200 km ) was named D '' . </P>
what is the name of the boundary between the mantle and the outer core
what is the name of the boundary between the mantle and the outer core
core -- mantle boundary
core -- mantle boundary