Core–mantle boundary Core–mantle boundary 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 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
What Shall We Do Now? the form of a fist that becomes a hammer (a hammer that would reappear in the animated sequence of "Waiting for the Worms"). "What Shall We Do Now?" would be performed at all concerts for "The Wall", and so appears on "Is There Anybody Out There? The Wall Live 1980–81". It was also included in Waters' 1990 "The Wall" Concert in Berlin, therefore appears on the album "The Wall – Live in Berlin". Waters also performed it on his 2010-2013 tour. What Shall We Do Now? "What Shall We Do Now?" (working title "Backs to the Wall") is a song