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
What We Do in the Shadows What We Do in the Shadows A documentary crew (who are wearing crucifixes) follows four vampire roommates—Viago, Vladislav, Deacon, and Petyr—who share a flat in the Wellington suburb of Te Aro. Although Viago, Vladislav and Deacon are all several centuries old, they have retained normal human appearances, but the 8,000-year-old Petyr resembles Count Orlok and acts more savagely than the younger vampires. Each night, Viago, Vladislav, and Deacon prowl the streets of Wellington searching for people to kill, but they must stay in the flat during the day to avoid sunlight—which is lethal to vampires—and thus have not adapted to