Through seismology, the study of earthquakes, we know that the earth is vast. Nevertheless, it still moves. Measurements taken during earthquakes have revealed that the earth has a number of outer 'skins', like the skins of an onion. The outer gaseous layer is about 1100 kilometres thick and is what we call the atmosphere. The air we breath is part of this. The hydrosphere consists of all the oceans, seas and lakes on earth. Interestingly, water makes up about 70 percent of the earth.