The Earth’s Structure A Journey to the Center of the Earth The Interior of the Earth The Earth’s Layers Earth can be divided into three main layers – the crust, mantle and core. The layering is due to differences in density Temperature and pressure in Earth’s interior increase with depth The Crust Rocky outer layer of Earth Made up of Silicates Two types of Crust Continental Crust – rocks that make up continents; thickness between 8 -75 km Oceanic Crust – rock that makes up ocean floor; average thickness 7 km The Mantle A thick layer of hot semi-solid dense rock Approximately 2850 km thick Composed of mostly iron, magnesium and aluminum. Makes up about 84% of Earth’s volume “Sub Layers” in the Crust & Mantle Lithosphere – composed of the oceanic and continental crust and the rigid upper mantle; thin outer shell of Earth; broken up into “plates”. Asthenosphere – softer and weaker rock in the mid-mantle; can flow slowly when under pressure Mesosphere – stronger lower part of the mantle The Core A large sphere of metal that occupies Earth’s center Composed mostly of iron and nickel Divided into 2 parts: Outer core – composed of liquid metal; 2260 km thick Inner core – solid due to very high pressure; 1220 km thick How do Scientists study Interior of Earth? Use of Seismic Waves 2 Types of Seismic Waves: S & P waves P waves: Travel through solids, liquids and gases Faster than S waves S waves Travel only through solids Speed and direction of both waves are affected by the composition of material they are traveling through Shadow Zones Locations on Earth’s surfaces where neither S or P waves are detected S waves will not travel through liquid core P waves speed and direction change causing them to bend