Transcript Section 1
The Layers of the Earth © Copyright 2006. M. J. Krech. All rights reserved. Earth’s Interior • Geologists have used two types of evidence to learn about Earth’s interior. • Direct evidence: Rock samples • Indirect evidence: Seismic waves Rock Samples • Geologists have drilled holes as deep as 12.3 Km into Earth. • They obtained clues of structure and conditions inside Earth. • Laboratory rock samples are squeezed with great force using laser beams. Seismic Waves • Geologist have recorded seismic waves and study how they travel through Earth. • Finding clues based in the speed and the path seismic waves take. When the waves reach specific depth the path change. Layers of Earth • • • • • • Three layers: crust, mantle and core. The layers vary greatly in: Size Composition Temperature Pressure Pressure • The deeper inside Earth, more pressure on the mass of rocks. • Pressure is a force pressing on an area. Temperature • Temperature inside Earth increases as depth increases. • Beneath earth surface rock is cool, but 20 meters down the rock starts to get warmer. • For every 40 meters down , the temperature increases 1 Celsius degree. • The high temperatures inside Earth are the results of great rock pressure, energy released from radioactive elements. Age of Earth • Earth was formed 4.6 billions years ago. The Four Layers The Earth is composed of four different layers. The crust is the layer that you live on. The mantle is much hotter and has the ability to flow. The outer core and inner core are even hotter with pressures so great you would be squeezed into a ball smaller than a marble if you were able to go to the center of the Earth! The Crust The Earth's Crust is like the skin of an apple. It is very thin in comparison to the other three layers. The crust is only about 5- 80 Km. It is thickest under the mountains ( continental crust ) and thinnest beneath the ocean. (oceanic crust). The Crust • The oceanic crust is made of basalt ( fine, dark rock) • The Continental crust is made of granite ( coarse, light rock). • Both rocks are Igneous. The Crust The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates. The Lithospheric Plates The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semi-rigid asthenosphere. The Mantle • The mantle is made of hot rock , but solid, Scientists divide the mantle into layers based on the physical characteristics of those layers. • Overall the mantle is about 3,000 Km thick. The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid strong, brittle rock called the Lithosphere. Earth’s lithosphere is nearly 100 Km. thick. The Asthenosphere The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight and pressure. This part of the mantle can bend as a metal spoon. Mesosphere • In this layer the mantle is hot but more rigid because of increasingly high pressure. This layer has a TRANSITION ZONE and includes the lower mantle which connects to the core. The Mantle The Mantle is the largest layer of the Earth. The middle mantle is composed of very hot dense rock that flows like asphalt under a heavy weight. The movement of the middle mantle (asthenosphere) is the reason that the crustal plates of the Earth move. Convection Currents The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over. Convection Currents The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. The crust gets a free ride with these currents, like the cork in this illustration. Safety Caution: Don’t get your face too close to the boiling water! The Core • The core is made of metals iron and nickel. It consists of two parts: • A dense, liquid outer core. • A dense solid inner core. The Outer Core The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of molten metals: nickel and iron. The Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move like a liquid, but are forced to vibrate in place like a solid. The core also contains: oxygen, sulfur and silicon. The Core and Earth’s Magnetic Field • Scientists believed that movement in the liquid outer core creates Earth’s magnetic field. • The planet acts as a giant magnet. • Using a compass, the compass needle aligns with the lines of force in Earth’s magnetic field. The End BONUS: Answer this question: Have we ever seen part of the Mantle? Explain. © Copyright 2006. M. J. Krech. All rights reserved.