Earth is made up of layers: the crust, mantle, and core. The crust is the solid outer layer of Earth. Under the crust is the mantle, which is solid on top and soft below. The core is at the very center of Earth, is made of metals, and is soft on the outside and solid at the center. The crust and solid upper mantle are broken up into huge pieces called plates, which are carried along by movement of magma in the lower mantle. The place where the edges of two places meet is called a fault and is where earthquakes occur. As two plates move next to each other, the rough edges can get stuck together. When the plates let go at a fault, the sudden movement of the ground causes an earthquake. Earthquakes cause seismic waves, which are vibrations that transfer energy through the Earth from the source of the earthquake. When we feel an earthquake, we are feeling the vibration of the seismic waves. Earthquakes can be big and cause much damage or can be small. By studying earthquakes, geologists can learn about how Earth works and what the inside of Earth is like. Pronunciation guide. 24 pages filled with engaging, colorful illustrations. Reading Level 1-3, Interest Level 2-5.