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 Call of Earth The Call of Earth The Call of Earth (1992) is a science fiction novel by American writer Orson Scott Card. It the second book of the Homecoming Saga, a fictionalization of the first few hundred years recorded in the Book of Mormon. The book focuses on several key events that happen after Nafai, Elemak, Issib, Mebbekew, Zdorab and the father Volemak leave for the desert. Elemak has a dream from the Oversoul, foretelling Volemak's sons going back to the city of Basilica to get wives. The sons proceed to Nafai's and Issib's mother, Rasa, who is attempting to keep order