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Plate Tectonics

Plate Tectonics. http://www.freewebs.com/morganisrupert/597340[1].jpg. Earth’s Composition. http://pubs.usgs.gov/publications/graphics/FigS1-1.gif. View of Earth. Scientists think about the Earth’s layers in two ways: Composition Physical properties.

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Plate Tectonics

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  1. Plate Tectonics http://www.freewebs.com/morganisrupert/597340[1].jpg

  2. Earth’s Composition http://pubs.usgs.gov/publications/graphics/FigS1-1.gif

  3. View of Earth • Scientists think about the Earth’s layers in two ways: • Composition • Physical properties http://www.matter.org.uk/schools/Content/Seismology/earth_core.html

  4. Earth’s Chemical Composition • Crust: outermost layer 2 types: • oceanic crust: • Thickness:Up to 5-8 km thick • composition: mostly basalt • younger rocks • density: approx. 3.0 g/cm3 • Continental crust • thickness: up to 8-75 km (avg: 40 km) • composition: mostly granitic (silicates make up most of crust) • density: approx. 2.7 g/cm3 • older rocks • Mantle • Contains most of Earth’s mass • Core • made of iron, with small amounts of nickel.

  5. Earth’s Physical Properties • Lithosphere(rock sphere) • Outermost rigid layer of earth • Divided into tectonic plates • 2 parts: • Crust • Rigid upper mantle • Asthenosphere(weak sphere) • Soft layer of mantle on which lithosphere move • Soft rock that flows like “putty” • Mesosphere(middle sphere) • Strong lower part of mantle • Extends to from bottom of asthenosphere to the core • Outer Core • Liquid layer • Iron content • Inner Core • Solid, dense iron and nickel

  6. Discontinuity: Seismic waves change velocity • Gutenberg Discontinuity • Boundary between mantle and core • Separates lower mantle (solid) from outer core (liquid) • Mohorovicic Discontinuity • Boundary between crust and mantle • Separates the lower density crust from the higher density mantle

  7. 225 Million Years Ago, there was a supercontinent called Pangaea Click: Pangea Animation

  8. Crustal Movement 2. : • The first theory of crustal movement was introduced in 1915 by Alfred Wegener, and was called The Theory of Continental Drift http://www.eoearth.org/files/124901_125000/124947/250px-Wegener3.jpg

  9. Evidence for this Theory • Edges of continents fit together like puzzle pieces • Correlation of rock layers/fossils- Rock layers and fossils found on opposite sides of ocean basins match up • Mountain Chains- Some mountain chains seem to be continuous from continent to continent. • Climateevidence- Ancient climates were different from today. Ex: glacial deposits in tropical regions; coal deposits in Antarctica. • Crustalage- Rocks of the ocean basins are much younger than continental rocks.

  10. Puzzle Pieces that Fit http://pubs.usgs.gov/publications/graphics/apres.gif

  11. FOSSILS http://pubs.usgs.gov/publications/graphics/Fig4.gif

  12. Climate http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_pics/F1.6b.gif

  13. Sea-floor spreading • Sea Floor Spreading: • Theory that states that ocean floors are forming and spreading out from the ridges. • Convection cell: • Driving force for spreading theory. • Hot, molten material from the mantle pushes upward, cools and solidifies at the surface to form new ocean rock. • Currents are created because of density differences in magma.

  14. CONVECTION CURRENTS Click for Convection Cell Animation *10

  15. Click: Video Of Plate Tectonic and Convection Currents

  16. Evidence for Sea Floor Spreading • Igneous Rocks: • Age of rocks increases as distance from ridge increases • Paleomagnetism: • magnetic patterns are symmetrical (the same) on both sides of the spreading centers. As molten ocean rock cools, the magnetic minerals in the rock align themselves with the Earth’s magnetic field. If the magnetic field is opposite what it is today, the minerals will point to the south magnetic pole. The ocean rocks show that during past history, Earth’s magnetic field has reversed a number of times.

  17. PALEOMAGNETISM – Each side of the Mid-Atlantic Ridge shows the same magnetic reversals. Click for Paleomagnetism Animation Click for Paleomagnetism Video

  18. Click: Video: Sea Floor Spreading- Bill Nye

  19. Plate Tectonics • Plate Tectonics: • Theory that Earth’s lithosphere is divided into tectonic plates that move around on top of asthenosphere. Text Pacific Plate is the largest plate http://www.extremescience.com/graphics/platetecmap.gif

  20. Major Plates of the World

  21. Plate Boundaries All plates have boundaries with other plates Three main types http://geology.csupomona.edu/drjessey/class/gsc101/boundaries.gif

  22. Continental-Continental Convergence • Mountain building • Folded mountains • Thrust-faulted mountains • Both plates are of equal density so they push into each other pushing crust up. http://pubs.usgs.gov/publications/graphics/Fig21contcont.gif

  23. Oceanic-continental convergence • Oceanic plate is more dense, so it sub ducts under the continental crust • Causes trenches • Longest-Peru/Chile • Deepest- Mariana • Place of earthquakes and volcanoes • Called a subduction zone • Destroys crust http://pubs.usgs.gov/publications/graphics/Fig21oceancont.gif

  24. Oceanic/Oceanic Convergent When two oceanic plates collide one plate slides under the other. Volcanoes form on ocean floor Could form volcanic island arc http://www.doeacckolkata.in/Piyali-geography/boundary2.jpg

  25. Convergent Boundary Video • Click: Convergent Boundary Formation

  26. Divergent Plates Rift Valley in Iceland • Plates move away from each other. • Forming • New crust • Mid ocean ridges • Rift valleys • Fissure volcanoes • Flood lavas http://pubs.usgs.gov/publications/graphics/lava_fountains.gif http://pubs.usgs.gov/publicatios/graphics/Fig16.gif

  27. Rift Valleys on Land Land is thinning- eventually will sink/break and fill with water http://www.etravelphotos.com/photos/2003ea/2003ea-001-03s-w.jpg

  28. Divergent Plate Boundaries – Pull Apart Click for Divergent Plate Video http://geology8b-9.wikispaces.com/file/view/d.jpg/88987877/d.jpg

  29. Divergent – Mid-Atlantic Ridge Click: Formation of Ocean Crust Click: Process of Rifting http://geology.wr.usgs.gov/parks/pltec/noaaMidAtlanticRidgeL.jpg

  30. Transform Boundaries • When two plates slide past each other horizontally. • Strike slip faults • San Andreas Fault http://pubs.usgs.gov/publications/graphics/San_Andreas.gif

  31. Summary of Types of Plate Boundaries Click: Summary Video of Plate Boundary Formation Table 2-1, p. 47

  32. Show Animations for Plate Boundaries • Click: Plate Boundary Animations

  33. Hot Spots • Areas that lie farfrom plate boundaries • Magma rises to surface • As plate moves, volcano becomes inactive • Creates volcanic mountains • Hawaii Click: Hot Spot Formation http://www.galapagosonline.com/Galapagos_Natural_History/Geology/HotSpot.jpg

  34. Click: Video Hotspot Volcanism

  35. Evidence of Crustal Activity • Deformed Rock Strata • Originally, sedimentary rocks form flat, horizontal layers However, observations made of Earth’s surface indicate that original rock formations have been changed through past Earth movements • This includes • Tilting: Rock layers are found at an angle to their original formation • Displaced fossils: • Shallow water fossils have been found at high elevations, and deep water fossils have been found in shallow water areas. This means the crust has been moved.

  36. Stress (Force) on Rocks http://scign.jpl.nasa.gov/learn/plate5.htm • Compression • Squeezing of rocks as when plates collide • Tension • Forces act to stretch object as when divergent plates move apart • Shear • Causes rock to be distorted https://www.classzone.com/books/earth_science/terc/content/investigations/es1102/es1102page02.cfm http://www.teachengineering.org/collection/cub_/lessons/cub_images/cub_rock_lesson01_fig1.gif

  37. Faulting • Pressure on rock layers causes them to break. • The boundary between the broken layers is called a fault • 3 types of faults http://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Barns_grand_tetons.jpg/284px-Barns_grand_tetons.jpg

  38. The force of tension causes normal faulting. Normal faulting is when the hanging wall moves downward. This type of faulting is common at divergent plate boundaries. Examples of this type of faulting are the Sierra Nevada mountains and the eastern border of California. 1. Normal http://www.nasa.gov/images/content/65877main_Foot_Hang_Wall.gif

  39. Folding occurs when rock layers in Earth’s crust bend due to stress

  40. 2. Reverse • The force of compression causes reverse faulting. • Reverse faulting is when the hanging wall moves up. • This type of faulting is common at convergent plate boundaries. • An example of this faulting is the Rocky Mountains.

  41. Reverse fault -The footwall is on the left. The beds indicate that the hanging wall has risen relative to the footwall.

  42. 3. Strike Slip • The force of shearing causes strike-slip faulting. • Movement along this type of fault is not up and down, but sideways. • This type of faulting is common at transform plate boundaries. • Examples of this type of faulting is the San Andreas fault.

  43. Aerial view of right-lateral strike-slip fault, southern Nevada.

  44. Faults! How Do They Move? • Click for Faults Video • Click for Fault Animations

  45. Video Lecture of Stress/ Faults • Click: Video Review of Stesses, Faults and Deformation

  46. Tracking Tectonic Plate Motion • Today scientists use the GPS (Global Positioning System) to track the motion of tectonic plates • We can measure plate movement accurately!

  47. Folding: • Rock layers are warped, or bent as a result of compression • Types of folds • Anticlines: arching up of rocks • Synclines: down-folds or troughs http://marlimillerphoto.com/images/SrD-02LR.jpg

  48. Appalachian Mountains • Formed originally from accumulated sediments • Tectonic processes folded the layered sediments into mountains • Evidence: shallow water fossils in the mountains http://appvoices.org/images/landingpg_mountains4.jpg

  49. Appalachian Mountains –how did they form?

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