1. 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. 2 Chapter Outline The Dynamic Earth Plate Tectonics: A Unifying View of Earth Another Look at Volcanoes and Earthquakes

3. 3 The Dynamic Earth

4. 4 Small-scale changes –Construction site Erosion by rain Large-scale changes –Volcanoes –Earthquakes –Erosion

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

6. 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. 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. 8 Ocean Floors Mapping –Ocean floor dynamic Canyons, mountains Mid-Atlantic Ridge –Earthquakes, volcanoes, lava flows

9. 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. 10 Magnetic Reversals

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

12. 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. 13 Plate Tectonics: A Unifying View of Earth

14. 14 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

15. 15 Earth’s Plates

16. 16 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

17. 17 Plate Boundaries Three Main Boundary Types –Divergent –Convergent –Transform

18. 18 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

19. 19 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

20. 20 Transform Plate Boundary Two plates move past each other –NOT smooth –Earthquakes as a result of movement

21. 21 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

22. 22 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

23. 23 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

24. 24 Seismology: Exploring Earth’s Interior with Earthquakes

25. 25 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