Structure of the Earth 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
What Hurts the Most hip-swiveling chorus after a flurry of robotic drum beats is certainly a good giggle." Kurt Kirton of About.com named it one of the album's standout tracks. Chuck Taylor of "Billboard" gave "What Hurts the Most" a positive review, writing that "this track is remixed into a frothy uptempo anthem, complete with requisite percussive thump and an exulted vocal (with 12 mixes in all) that leaves the lyric's potential heartbreak in the dust." Taylor ended his review, asking "Wouldn't it be wondrous if American programmers renewed their vow in 2008 to put variety on the airwaves—or do we really need a