Earth's Interior.pdf

the Earth’s InterioR EXPLORING INSIDE EARTH Geologists have used two main types of evidence to learn about Earth’s interior: direct evidence from rock samples and indirect evidence from seismic waves. 4 5  Sometimes, forces inside Earth blast rocks to the surface from dept...

the Earth’s InterioR EXPLORING INSIDE EARTH Geologists have used two main types of evidence to learn about Earth’s interior: direct evidence from rock samples and indirect evidence from seismic waves. 4 5  Sometimes, forces inside Earth blast rocks to the surface from depths of more than 100 km. These rocks provide more information about Earth’s interior. 6  Since geologists cannot look inside Earth, they must rely on indirect methods of observation. When earthquakes occur, they produce seismic waves. Geologists record seismic waves and study how they travel through Earth. The speed of the seismic waves and the paths they take reveal the structure of the planet. 7  Knowing how the waves behave as they move through different materials enables us to learn about the layers that make up the Earth. Seismic waves tell us that the Earth’s interior consists of a series of concentric shells, with a thin outer crust, a mantle, a liquid outer core, and a solid inner core.  P waves, meaning primary waves, travel fastest and thus arrive first at seismic stations. The S, or secondary, waves arrive after the P waves.  WHAT ARE THE LAYERS OF THE EARTH THAT YOU KNOW?  The three main layers of Earth are the crust, the mantle, and the core. These layers vary greatly in size, composition, temperature, and pressure.  The crust is the layer of rock that forms Earth’s outer skin. The crust is a layer of solid rock that includes both dry land and the ocean floor. This layer of the Earth is much thinner than the layers beneath it.  The crust beneath the ocean is called oceanic crust, which consists mostly of rocks such as basalt. Basalt is dark rock with a fine texture.  Continental crust, crust that forms the continents, consists mainly of rocks such as granite. Granite is a rock that usually is light in color and has a coarse texture.  Below Earth’s crust is the mantle. Earth’s mantle is made up of rock that is very hot, but solid. Scientists divide the mantle into layers based on the physical characteristics of those layers. Overall, the mantle is nearly 3000 km thick.  The upper most part of the mantle and the crust together form a rigid layer called the lithosphere. In Greek, “lithos” means “rock.”  Below the lithosphere is a layer that is hotter and under increasing pressure. This soft layer of the mantle is called the asthenosphere. In Greek, “asthenes” means “weak.” Although this layer is softer than the rest of the mantle, it is still solid.  Below the asthenosphere, the mantle is solid. This solid material extends all the way to Earth’s core.  Beneath the mantle is Earth’s core. The core is made mostly of the metals iron and nickel. It consist of two parts- a liquid outer core and solid inner core.  The outer core is a layer of molten metal that surrounds the inner core. Despite pressure from the rock above, it is liquid.  The inner core is a dense ball of solid metal. In the inner core, extreme pressure squeezes the atoms of iron and nickel so much that they cannot spread out and become liquid. the Earth’s InterioR