  Scientists study layers of rocks to learn about the earth and how it has changed. They know that if layers are undisturbed, the oldest rocks are on the bottom and the yo … ungest rocks are on top.They know how old each layer is in relation to the other layers.+ 12 others found this useful. Scientists study layers of rocks to learn about the earth and how it has changed. They know that if layers are undisturbed, the oldest rocks are on the bottom and the yo … ungest rocks are on top. They know how old each layer is in relation to the other layers. + 12 others found this useful.