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? What Shall We Do Now? "What Shall We Do Now?" (working title "Backs to the Wall") is a song by Pink Floyd, written by Roger Waters. It was originally intended to be on their 1979 album "The Wall", and appeared in demo versions of "The Wall", but was omitted due to the time restraints of the vinyl format. In its place is a much shorter song, titled "Empty Spaces", which segues directly into "Young Lust". This was a last-minute decision; the album's sleeve notes still feature the song in its track listing, and include its lyrics. The beginning of the