Structure of the Earth What is the earth like below its surface? Inside the Earth 1:34 What makes up the interior of our planet? Compiled by Susan Weidkamp
Chapter 22 Objectives To observe how change is dependent on depth. The chemical makeup of the earth changes as you go deeper. The density of materials increase with depth. Temperature and pressure increase with depth. To explain why these changes are observed. To learn how models are used in science. 2
Earth has a few well kept secrets 3
Chemical vs.physical Chemical layers refer to the composition or make up of the earth s interior. Physical Layers refer to the state of matter such as solid, liquid, or in between called plastic. 4
6. The Moho Boundary Found between the chemical layers of the crust and the mantle. Andrija Mohorovicic (Mo-ho-ro-vi-chic) discovered a boundary between the crust and the mantle. The boundary is now known as the Moho, or Mohorovicic Discontinuity. 5
7. Roughly, how hot is the Earth s core? 6
Layers of the Interior of an Egg Chemical Layers of an egg: Physical Layers of an egg: Crust-solid Crust-CaCO 3 Egg whiteamino acids & proteins Yolk- Lipids Fatty acids Egg white- Liquid Yolk- Liquid 7
How do the chemical layers change in an egg as you go deeper? The type of compound changes from calcium carbonate, CaCO3 to Proteins and the inner yolk is mostly lipids or fat. How do the physical layers change in an egg as you go deeper? The state changes from outer rigid solid to liquid egg white and yolk. 8
Compare the physical layers on right to the chemical layers. How are they different? How are they similar? Interior of the Earth MOHO 9
8. How do the chemical layers change in the Earth as you go deeper? The type of material changes from compounds like silicates to a core of mostly elemental and metallic iron. 9. How do the physical layers change in the Earth as you go deeper? The state changes from the outer rigid crust a solid, to the plastic asthenosphere to the liquid core and the inner solid core. 10
Why are there more physical layers than chemical layers? 10. Chemical layers: Crust- Silicates of Al, Fe and Mg Mantle-Silicates of Fe and Mg Core- Metallic Iron 11. Physical layers: Lithosphere rigid solid Asthenosphere- plastic Mesosphere- solid Outer Core- Liquid Inner Core- Solid 11
Scale of the Interior 12
How does the temperature change the deeper you go? The change in temperature and pressure affect the state of the interior of the Earth and density probably has the most effect on the chemical layers. 13
Check your neighbor How do the chemical layers change as you go deeper? How do the physical layers change? Name the chemical layers: Name the physical layers: 14
How do we really know what the center of the earth is like? We have to make an educated guess Or we go to the movies! 15
Ch. 22 Objectives Part 2 How do scientists study the earth s interior? Identify two types of seismic waves. Explain how scientists make inferences about the earth s core. Infer characteristics of an object through indirect observation. 16
Indirect observations Example #1 WIND When you do not actually observe the wind, you see only its effects as the branches of a tree move. The moving branches are the indirect observation. The wind is the inferred characteristic. 17
What is the core of the earth like? A. Creamy Chocolate B. Chewy Nougat C. Soft Caramel D. Hard Rock Candy 18
What is the deepest hole in the earth? 12,345 meters or 7.67 miles Sakhalin-1 19
Density Puzzle Inference #1 Density of the earth equals the earth s mass divided by its volume, or 5.5 g/cm 3 Core must me more to average 5.5 g/cm3 Average rocks found in the crust have a density of 3.5 g/cm3. What must be the core s density, more than 5.5 or less than 5.5? 20
Light energy waves bend Light will bend and reflect at the interfaces between different materials. Do seismic energy waves bend like light? Yes! 21
Seismic Waves P waves are PRIMARY WAVES They travel like a slinky. They are the fastest, and are called: S waves are shear or SECONDARY WAVES They travel like a snake. They are second fastest and are called: http://www.geo.mtu.edu/upseis/waves.html 22
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Inference # 2 Earth s Interior has several layers. Evidence: P-waves bend at every new layer. S-waves bend in solid layers, but stop at liquid layers 24
The Moho Boundary Inference #3 Between the chemical layers of the crust and the mantle. Andrija Mohorovicic (Mo-ho-ro-vi-chic) discovered a boundary between the crust and the mantle. He found seismic waves speeded up at a depth between 30-35 km below the surface. Why would they speed up? A. The earth becomes hotter the deeper you go. B. The earth becomes denser the deeper you go. C. The pressure increases so particles are closer together. The boundary is now known as the Moho, or Mohorovicic Discontinuity. http://www.infp.ro/labs/file2.htm 25
Evidence from Seismic Waves Recordings of seismic waves from earthquakes gave scientists a puzzle: A shadow zone (no waves) appeared at 105 degrees. 26
Slower, Shear, S waves offer a clue Transverse waves (S waves) as cannot travel through liquids. Liquids have weak forces of attraction between the particles, and these waves break up when they arrive. This explains why there is a large S SHADOW ZONE. 27
Inference # 4 Evidence of the earth s core Seismic waves bend as they pass through interior; this creates a shadow zone. The p shadow zone indicates the size of the core. The s shadow zone indicates the physical state of the outer core- liquid. 28
The Shadow Zone Puzzle The area beyond 105 degrees distance forms a shadow zone. At larger distances, some P waves would arrive, but still no S waves. Only slow traveling surface waves reach this area traveling through a thin layer of crust. Seismic waves bend at an interface, or chemical layer. 29
Inference #5 How big is the Earth s core? Using the 105 degree angle of the shadow zone, and the Earth s radius of about 6350km, draw a a right triangle. Then calculate: Radius of core 6350 km = cosine of 52.5 degrees Cosine of 52.5 =.60876 Core s radius = 3870km (52.5 degrees is half of 105 degrees, and cosine = adjacent / hypotenuse) 30
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IRIS video Clip explaining shadow zone Turkey Part II 32
Propagation of Seismic Waves 33
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How Earthquakes are located 35
Seismic Wave Analysis The time between the two arrivals is exactly 10 seconds. The ratio of velocities is 8.7 km/sec. The product of these two values = 87 kilometers or the distance between the seismometer and the earthquake. 36
Using a Time-Distance Graph 37
Check your neighbor How did scientists discover the Earth s core? How are P waves different from S waves? What clue s did the shadow zone tell us? About how big is the Earth s core? Where is the Moho found? Between the crust and the mantle 38
Physical Layers Lithosphere - Lithos = Rock, or stone Asthenosphere-Sthenos = strong, asthenos = not strong ( prefix a negates) 39
The Lithosphere Oceanic Crust- usually found under oceans, and near the edge of continents. Continental Crustusually found in continents, forming plains, and mountains. 40
Coast of the UK 41
Oceanic Crust Oceanic crust is mostly made of dark rocks like basalt and gabbro. 42
Continental Crust Continental crust is less dense than oceanic crust. It contains more silicon, oxygen and aluminum. Most of the rocks are made of granite and rhyolite. 43
What causes new crust to form? What causes the volcanoes in the Pacific Rim? 44
Last Oregon Tsunami 1700 45
Movement in the Asthenosphere How do temperature changes affect the movement of matter in the mantle? Hot matter rises, cools then sinks back. 46
Convection Cell 47
Convection Currents Interior of Earth 48
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Plume rising through a layered viscosity mantle The plume encounters a change in viscosity. It passes from the lower mantle to the upper mantle. Now under less pressure, it becomes thinner (less viscous) and faster. 50
Convection of Mantle animation More Interactive animations 51
Viscosity Changes in viscosity or thickness occur due to changes in temperature. For example hot maple syrup is less viscous (thinner) than cold syrup. Question #23 52
Check your neighbor What makes up the lithosphere? What is the difference between oceanic crust and continental crust? Describe the convection current within the asthenosphere. How do changes in temperature affect the viscosity of the mantle? What are the pros and cons of using computer models to simulate the interior of the earth? 53
References 1. Earth Sciences Pictures. NASA Space Science Photo Gallery. May 7, 2001. http://pao.gsfc.nasa.gov/gsfc/earth/pictures/earthpic.htm 2. Louie, John N. Earth s Interior. http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html 3. Seismic Waves. Alaska Earthquake Information Center. Geophysical Institute. University of Alaska. May 7, 2001. http://www.aeic.alaska.edu/input/lahr/waves/waves.html 4. Investigating Earthquakes through Regional Seismicity. Southern California Earthquake Center. May 7, 2001. http://www.scecdc.scec.org:3128/module/tableofc.html 54
References Continued 5. Camp Breakfast. Maple Grove Farms. May 7, 2001. http://store.yahoo.com/maplegrove/campbreakfast.html 6. Some unanswered questions. USGS. May 7, 2001. http://pubs.usgs.gov/publications/text/unanswered.html#anchor199283 10 7. Mantle Convection Subgroup. May 7, 2001. http://wwwrses.anu.edu.au/gfd/gfd_other_pages/convection_demo/de mo_page_2.html 8. Mantle, Plumes, Plate tectonics and Hot spots.may 7, 2001 http://icdp.gfz-potsdam.de/html/hawaii/objectives/plumes.html 55