They came to the conclusion that the outer core must be liquid because S waves do not pass through it, but P waves do. By observing many seismic waves from earthquakes, the scientists have been able to measure the density of many parts of the earth (i.e. core, crust, and mantle)
In the book "Things Fall Apart" by Chenua Achebe. Cowries, the shell of a type of mollusk, are the primary currency in many of the african villages. historical the shell have been found across subsaharan Africa where they were obtained through trade with travelers from farther east along the coast and possibly asia.
the demand can be said to be inelastic
