Chapter 4

1. Chapter 4 Introducing the Earth

2. Layers of the Earth(from the outside to the inside) • Crust • Mantle • Lithosphere • Asthenosphere • Mesosphere • Core • Inner core • Outer Core

3. Convection in the Mantle • The movement of energy from a warmer object to a cooler object is called heat transfer • Three types of heat transfer: • Radiation-transfer of energy that is carried in rays • Ex. Heat from the sun • Conduction-energy transfer between things that are touching • Convection-energy transfer by the movement of particles—liquid or gas • Caused by three things • Heating and cooling • Changes in density • Force of gravity

4. Convection in the Mantle • Convection occurs due to differences in DENSITY –how much mass there is in a given volume • Lets look again at the pot, pretend we are cooking soup. Here is how it works • The soup at the bottom gets hot and expands, its density decreases • The hot soup then rises to the top and floats over the cooler, more dense soup • Once at the top the hot soup cools and becomes more dense which then causes it to sink • It is then warmed again and the process starts over

5. Convection in the Mantle • How does that the soup relate to the mantle? • Heat from the mantle itself and the core acts like the heat from the stove to create convection currents in the rock • How can rock flow? • Heat and pressure have caused the rock to warm and flow very slowly • Convection currents cause the rock to flow just like the soup in the pot but on a much slower scale • Convection currents also occur in the outer core, these are thought to cause the Earth’s magnetic field.

6. Earth’s Interior • Three main layers 1.) Crust-solid rock, includes dry land and ocean floor, composed of silicon and oxygen, 5-40 km thick thickest—under mountains thinnest—below ocean • Oceanic crust-made of basalt (dark, fine grained rock), more dense than Continental crust • Continental crust- composition varies greatly, mostly granite (light in color, coarse grained), less dense than oceanic crust • Both granite and basalt are composed largely of oxygen and silicon

7. Earth’s Interior 2.) Mantle- 3000 km thick, calcium / iron / magnesium aluminum silicates • Upper mantle • Lithosphere-uppermost mantle and crust, strong hard and rigid • Asthenosphere-hotter, increased pressure—less rigid, over thousands of years can bend like metal • Lower Mantle • Mesosphere-hot, more rigid than asthenosphere due to increase in pressure, transition zone found here

8. Earth’s Interior • Mohorovicic discontinuity, or simply the Moho-boundary between crust and mantle • We know its there because it changes the speed and direction of seismic waves

9. Earth’s Interior 3.) Core-mostly iron and nickel, same temperature as the surface of the sun, 5430oC • Outer core-2300 km thick, molten metal • Inner Core-1200 km thick, solid metal • Earth’s Magnetic Field- --Movement in the liquid outer core create magnetic field --Earth is like a giant bar magnet --When you use a compass, the needle aligns with Earth’s magnetic north pole (not the same as the geographic north pole)

10. How do we know these layers exist? • Rock samples (direct evidence) • Holes drilled to about 12.3 km to bring up rocks • Volcanoes shoot rocks into the air from a depth of more than 100 km • Geologists recreate conditions in Earth—lasers and pressure • Seismic Waves (indirect evidence) • Waves produced by earthquakes • Speed and direction of waves give indication about structure of Earth’s interior • For example, surface waves from a powerful earthquake near Northridge, California, in 1994 took 30 minutes to reach a point about 6,700 kilometers (4,163 miles) away, but it took P-waves only 10 minutes and S-waves just under 20 minutes to travel the same distance. • Near the surface, P-waves travel about 6 kilometers per second through the ground. At a depth of about 35 kilometers they travel about 8 km/s, indicating that the waves have reached denser material at that point.

11. Cool facts about the interior • As we move deeper • Density increases • Pressure increases • Temperature increases • High temperature is a result of • pressure squeezing the rock • Release of energy from radioactive substances • Heat left over from origin of earth These convection currents cause Earth’s magnetic field convection cannot take place without a source of heat. Heat within the Earth comes from two main sources: radioactive decay and residual heat. Radioactive decay, a spontaneous process that is the basis of "isotopic clocks" used to date rocks, involves the loss of particles from the nucleus of an isotope (the parent) to form an isotope of a new element (the daughter). The radioactive decay of naturally occurring chemical elements -- most notably uranium, thorium, and potassium -- releases energy in the form of heat, which slowly migrates toward the Earth's surface. Residual heat is gravitational energy left over from the formation of the Earth -- 4.6 billion years ago -- by the "falling together" and compression of cosmic debris. How and why the escape of interior heat becomes concentrated in certain regions to form convection cells remains a mystery. http://pubs.usgs.gov/gip/dynamic/unanswered.html#anchor19928310

12. The Earth System • System-group of parts that work together as a whole • The Earth system involves a constant flow of matter through different parts. • This is not possible with out energy • Energy-the ability to do work • Where does the energy that drives the Earth system come from? • Heat from the sun • Heat flowing out from Earth as it cools • Earth contains air, water, land and life. Each of these forms its own “sphere” • Atmosphere-thin envelope of gases around Earth • Geosphere-Earth's interior, rocks and minerals, landforms and the processes that shape the Earth's surface. • Hydrosphere-All the waters on Earth’s surface • Biosphere- made up of all that is living on earth, from the smallest bacterium to the largest whale.

13. The Earth System • What part of this system represent Earth’s 4 spheres? • What is one source of energy for this system? • How is the aquarium similar to and different from Earth’s system?

14. The Earth System • Feedback—information about a change in a system • Positive-increase the effects of a change • Earth's temperature and the subsequent formation of sea ice are controlled by a positive feedback loop. A drop in Earth's temperature can result in the formation of sea ice. Sea ice reflects the sun's light back toward space. An increase in sea ice would result in more of the sun's light being reflected back into space. This would result in further cooling of Earth's atmosphere and the formation of more sea ice. Thus, the presence of sea ice--because of a cool climate--reinforces the further cooling of Earth's climate and the formation of more sea ice. • Negative-slow down the effects of a change • Earth's temperature is also controlled by negative feedback loops. Water vapor and other heat-trapping gases such as carbon dioxide (CO2) are released into the atmosphere from power plants and automobiles. These heat-trapping, or greenhouse, gases can lead to an increase in Earth's average temperature. An increase in Earth's temperature can lead to more evaporation and ultimately increased cloud cover. Clouds reflect the sun's energy to space before it can reach Earth's surface. The result is global cooling. Thus, increased cloud cover that results from global warming can lead to global cooling, which lessens the impacts of greenhouse gases on Earth's temperature.

15. Constructive/Destructive Forces • The Earth’s surface is constantly being created and destroyed • Constructive force—build up Earth’s surface • Mountains, deposition, volcanoes • Destructive force-destroy, wear away Earth’s surface • Erosion, weathering • Erosion-wearing down and carrying away of land by natural forces • Forces of erosion: • Wind • Water • Ice