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)
By giving people more education, and remember they are using their money to give everyone else a bigger and brighter future of education, health, and more.
