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Inside Earth |
Scientists learn about Earth by studying earthquakes. An earthquake is a movement or vibration in Earth caused by the release of stored energy in Earth’s outer layer. Scientists use a seismograph to detect, measure, and record the energy of earthquake vibrations.
Rocks in the outer layer that break are called a fault. The focus is where the movement begins. Seismic waves are energy released as vibrations. The farther waves are from the focus, the weaker they become. A seismograph records different wave strengths. It can also tell about Earth’s interior since different waves travel at different speeds. Primary waves called P waves are the fastest seismic waves. They can travel through solids, liquids, and gases. Secondary waves called S waves travel slower than P waves and can travel through solids. Surface waves called L waves are the slowest waves and cause damage.
Earth has four layers which are the crust, mantle, outer core, and inner core. The crust is thicker under the continents than under the oceans. The mantle is the thickest layer. Rocks can move in this region because of great pressure and high temperature. The outer core is the liquid layer below the mantle and is made up of melted iron. The inner core is the sphere of solid material at Earth’s center. |
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