As scientists studied earthquake waves, they noticed something interesting The speed of the waves changed as they traveled through Earth. The path of the waves also changed. These changes happen tha because Earth is made of layers. The layers de have different compositions and different densities. Density is the amount of mass per ele unit volume of a material. These differences the make the earthquake waves slow down, speed up, or change direction By tracking earthquake waves. scientists were able to figure out the structure of Earth's layers. Scientists also studied meteorites, which are rocky objects H that fall to Earth from space. Meteorites. formed at the same time Earth formed. They formed from the same materials. So meteorites also provide clues to the inside of Earth. Using these clues, scientists found that Earth's layers vary in temperature, pressure, and density