The Energy Dilemma: Seismic Evidence for Earth’s Internal Structure Reveals a Power Source During the early 1960s, seismologists studying earthquake seismic waves detected the layer configuration of the Earth’s crust, mantle, outer and inner core. They found that the crust and the upper most portion of the mantle actually acted together as a single brittle layer. They called this the lithosphere. More importantly, they discovered that under the lithosphere, a several hundred mile thick portion there existed a layer that of rock with fluid-like properties. They called this layer the asthenosphere. Although the rocks were solid, they acted as though they were plastic. This plastic layer became the key to explaining how continents moved.