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Plate Tectonics

This chapter explores the concept of plate tectonics and how the Earth is constantly changing due to the slow convection of hot rocks deep within the planet. It discusses the dynamic nature of the Earth, the evidence of Earth's inner forces through volcanoes and earthquakes, the movement of continents, ocean floor dynamics, magnetic reversals, rock ages, and new support for the theory of plate tectonics.

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Plate Tectonics

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  1. Plate Tectonics 5 November 2015 Chapter 17 Great Idea: The entire Earth is still changing, due to the slow convection of soft, hot rocks deep within the planet.

  2. Chapter Outline • The Dynamic Earth • Plate Tectonics: A Unifying View of Earth • Another Look at Volcanoes and Earthquakes

  3. The Dynamic Earth

  4. The Dynamic Earth • Small-scale changes • Construction site • Erosion by rain • Large-scale changes • Volcanoes • Earthquakes • Erosion

  5. The Case of the Disappearing Mountains • Erosion • Few hundred million years • Mountains continually forming • Earth’s surface is not static

  6. Volcanoes and Earthquakes-Evidence of Earth’s Inner Forces • Volcano • Magma breaks through surface • Earthquake • Rocks breaks along fault • Energy transmitted as wave • Richter scale

  7. The Movement of the Continents • F. Bacon • Continents like a puzzle • Wegener • Continental Drift • Continents in motion • Current Evidence • Ocean Floors • Magnetic Reversals • Rock Ages

  8. Ocean Floors • Mapping • Ocean floor dynamic • Canyons, mountains • Mid-Atlantic Ridge • Earthquakes, volcanoes, lava flows

  9. Magnetic Reversals • Earth’s magnetic field • Changes periodically • Magnetite • Crystals in lava align to magnetic field • Paleomagnetism • Seafloor Spreading • New rock comes to surface

  10. Magnetic Reversals

  11. Rock Ages • Radioactive Isotopes • Rocks near Mid-Atlantic Ridge younger • Rocks farther away older

  12. New Support for the Theory • Measuring motion of continents • Radio Astronomy • Measured arrival of radio waves • Repeated over several years • North America and Europe • Separating at 5 cm per year

  13. iClicker Question • The Great Smoky Mountains look different from the Rocky Mountains because: • A the Smokies are older and have been eroding away • B the Rockies are older and have grown taller • C the Smokies are younger and have not eroded the softer rocks away like the Rockies have

  14. iClicker Question • Most geological processes such as mountain building and erosion are very rapid by human standards. • A True • B False

  15. iClicker Question • No earthquakes greater than 9 on the magnitude scale have ever been recorded. • A True • B False

  16. iClicker Question • In 1912 a German meteorologist named Alfred Wegener proposed: • A Earth’s continents are in motion • B weather patterns are related to earthquakes • C a magnitude 10 earthquake would strike California in 2009

  17. iClicker Question • For most of the twentieth century, continental drift was regarded as a far-fetched exercise in theory, and few geologists paid much attention to it. • A True • B False

  18. iClicker Question • Before the ocean floors were mapped in the years following World War II, most scientists thought that the deep ocean bottoms: • A could not be reached • B contained mountains and deep valleys • C were simply flat plains

  19. iClicker Question • The longest mountain range on Earth is: • A the Himalayas • B the Mid-Atlantic Ridge • C the Rocky Mountains

  20. iClicker Question • The Earth’s magnetic field has always pointed in the same general direction. • A True • B False

  21. iClicker Question • Rocks near the Mid-Atlantic Ridge are very old, while rocks collected successively farther away from the ridge are successively older. • A True • B False

  22. iClicker Question • The shape of the continents, the magnetic stripe pattern on the ocean floor, and the relative ages of rocks on the ocean floor are all evidences for • A man’s influence on the Earth • B paleomagnetism • C continental drift • D tsunamis

  23. Plate Tectonics: A Unifying View of Earth

  24. Plate Tectonics • Plate Tectonics • Large-scale surface features • Related phenomena • Tectonic plates • Rigid, moving sheet of rock • Crust and upper mantle • Continental • 100 km thick • Lower density (granite) • Oceanic • 8-10 km thick • Dense rock (basalt) • Earth’s surface • ¼ continent, ¾ water

  25. Earth’s Plates

  26. The Convecting Mantle • Mantle convection • Motion driven by Earth’s interior heat energy • Sources of energy • Gravitational potential energy • Decay of radioactive elements • Movement • Heat moves to cooler regions • Convection cells in mantle • Very slow • 200 million years for one cycle

  27. Plate Boundaries • Three Main Boundary Types • Divergent • Convergent • Transform

  28. Divergent Boundaries • Characteristics • Volcanoes • Chain of mountains • Earthquakes • Seafloor spreading • Plates pushed apart • Old spreading centers • Located in middle of ocean • New spreading centers • May begin anywhere

  29. Convergent Plate Boundaries • Types • Oceanic-oceanic • Subduction zone • Deep oceanic trench • Island arc • Continental-continental • High, jagged mountain chain • Continental-oceanic • Subduction zone • Deep oceanic trench • Coastal mountain range

  30. Transform Plate Boundary • Two plates move past each other • NOT smooth • Earthquakes as a result of movement

  31. The Geological History of North America • Northeastern Canada and Greenland • Several billion years old • Western US • Terranes • Added to continent over time • Appalachian Mountains • Formed 450-300 million years ago • Continental-continental convergence zone • Rocky Mountains • 60 million years ago • Warping, folding and fracturing of continent • The Colorado Plateau • Gentle uplift • The Sierra Nevada • Molten rock pushed up sediments

  32. Another Look at Volcanoes and Earthquakes • Plates and Volcanism • Divergent Plate Boundaries • Convergent Plate Boundaries • Subduction zones • Hotspots • Source stationary, plates move • Chain of volcanoes • Earthquakes • At plate boundaries or elsewhere

  33. Seismology: Exploring Earth’s Interior with Earthquakes • Seismology • Study of sound vibrations within earth • Used to determine earth’s inner structure • Seismic waves • Compressional or longitudinal • P-waves (pressure waves) • Transverse or shear waves • S-waves

  34. Seismology: Exploring Earth’s Interior with Earthquakes

  35. Plate tectonics is involved in the formation of the three major categories of rocks • Igneous Rock • cooled from molten material • Sedimentary Rock • Layered eroded material formed by the action of wind, water, or ice • Metamorphic Rock • Rock that has been altered in the solid state by extreme heat and pressure

  36. iClicker Question • The central idea of plate tectonics theory is that • A the surface of the Earth is broken up into about a dozen large pieces • B the Earth is rigid and unchanging • C the continents are moving

  37. iClicker Question • Which type of plates are on average 8-10 km thick and made of dense rocks known as basalt? • A oceanic • B continental • C mountain

  38. iClicker Question • Which type of plates are on average 35km thick and made of lower-density rocks such as granite? • A oceanic • B continental • C mountain

  39. iClicker Question • What causes tectonic plates to move: • A solar energy • B oceanic wave and tidal motion • C mantle convection

  40. iClicker Question • Volcanoes are common in which geological situations? • A divergent plate boundaries • B convergent plate boundaries • C hot spots • D all of the above

  41. iClicker Question Rocks formed when molten material cools and solidifies are called A igneous rocks B sedimentary rocks C metamorphic rocks D fault rocks E scarp rocks

  42. iClicker Question • If a scientist predicted with 80% certainty that a major earthquake would strike your location in the next 30 days what would you do? • A leave the area • B ignore the prediction • C panic • D none of the above, take other action

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