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 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: –Athe Smokies are older and have been eroding away –Bthe Rockies are older and have grown taller –Cthe 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. –ATrue –BFalse

15 iClicker Question No earthquakes greater than 9 on the magnitude scale have ever been recorded. –ATrue –BFalse

16 iClicker Question In 1912 a German meteorologist named Alfred Wegener proposed: –AEarth’s continents are in motion –Bweather patterns are related to earthquakes –Ca 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. –ATrue –BFalse

18 iClicker Question Before the ocean floors were mapped in the years following World War II, most scientists thought that the deep ocean bottoms: –Acould not be reached –Bcontained mountains and deep valleys –Cwere simply flat plains

19 iClicker Question The longest mountain range on Earth is: –Athe Himalayas –Bthe Mid-Atlantic Ridge –Cthe Rocky Mountains

20 iClicker Question The Earth’s magnetic field has always pointed in the same general direction. –ATrue –BFalse

21 iClicker Question Rocks near the Mid-Atlantic Ridge are very old, while rocks collected successively farther away from the ridge are successively older. –ATrue –BFalse

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 –Aman’s influence on the Earth –Bpaleomagnetism –Ccontinental drift –Dtsunamis

23 Plate Tectonics: A Unifying View of Earth

24 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 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 –Athe surface of the Earth is broken up into about a dozen large pieces –Bthe Earth is rigid and unchanging –Cthe continents are moving

37 iClicker Question Which type of plates are on average km thick and made of dense rocks known as basalt? –Aoceanic –Bcontinental –Cmountain

38 iClicker Question Which type of plates are on average 35km thick and made of lower-density rocks such as granite? –Aoceanic –Bcontinental –Cmountain

39 iClicker Question What causes tectonic plates to move: –Asolar energy –Boceanic wave and tidal motion –Cmantle convection

40 iClicker Question Volcanoes are common in which geological situations? –Adivergent plate boundaries –Bconvergent plate boundaries –Chot spots –Dall of the above

41 iClicker Question Rocks formed when molten material cools and solidifies are called Aigneous rocks Bsedimentary rocks Cmetamorphic rocks Dfault rocks Escarp 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? –Aleave the area –Bignore the prediction –Cpanic –Dnone of the above, take other action