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
Salting the earth Salting the earth Salting the earth, or sowing with salt, is the ritual of spreading salt on conquered cities to symbolize a curse on their re-inhabitation. It originated as a symbolic practice in the ancient Near East and became a well-established folkloric motif in the Middle Ages. The custom of purifying or consecrating a destroyed city with salt and cursing anyone who dared to rebuild it was widespread in the ancient Near East, but historical accounts are unclear as to what the sowing of salt meant in that process. Various Hittite and Assyrian texts speak of ceremonially strewing salt, minerals,