Structure of the Earth easily than does the upper mantle (chemical changes within the mantle may also be important). The viscosity of the mantle ranges between 10 and 10 Pa·s, depending on depth. In comparison, the viscosity of water is approximately 10 Pa·s and that of pitch is 10 Pa·s. The source of heat that drives plate tectonics is the primordial heat left over from the planet’s formation as well as the radioactive decay of uranium, thorium, and potassium in Earth’s crust and mantle. The average density of Earth is . Because the average density of surface material is only around , we must
The Ego and Its Own is certainly true that we must first make a cause our own, egoistic cause, before we can do anything to further it. . . . [W]e are communists out of egoism also, and it is out of egoism that we wish to be human beings, not mere individuals... However, Marx and Engels would later collaborate on a lengthy criticism of Stirner's book in "The German Ideology" (1845, published 1932). The critique is a polemical tirade filled with ad hominem attacks and insults against Stirner (Marx calls him a "petty bourgeois individualist intellectual"). Stirner also had a lasting influence in the