Plate Tectonics Chapter 17 Great Idea: The entire Earth is still changing, due to the slow convection of soft, hot rocks deep within the planet. 1
Chapter Outline The Dynamic Earth Plate Tectonics: A Unifying View of Earth Another Look at Volcanoes and Earthquakes 2
The Dynamic Earth 3
The Dynamic Earth Small-scale changes Construction site Erosion by rain Large-scale changes Volcanoes Earthquakes Erosion 4
Erosion The Case of the Disappearing Mountains Few hundred million years Mountains continually forming Earth s surface is not static 5
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 6
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 7
Ocean Floors Mapping Ocean floor dynamic Canyons, mountains Mid-Atlantic Ridge Earthquakes, volcanoes, lava flows 8
Magnetic Reversals Earth s magnetic field Changes periodically Magnetite Crystals in lava align to magnetic field Paleomagnetism Seafloor Spreading New rock comes to surface 9
Magnetic Reversals 10
Rock Ages Radioactive Isotopes Rocks near Mid-Atlantic Ridge younger Rocks farther away older 11
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 12
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 13
iclicker Question Most geological processes such as mountain building and erosion are very rapid by human standards. A True B False 14
iclicker Question No earthquakes greater than 9 on the magnitude scale have ever been recorded. A True B False 15
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 16
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 17
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 18
iclicker Question The longest mountain range on Earth is: A the Himalayas B the Mid-Atlantic Ridge C the Rocky Mountains 19
iclicker Question The Earth s magnetic field has always pointed in the same general direction. A True B False 20
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 21
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 22
Plate Tectonics: A Unifying View of Earth 23
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 24
Earth s Plates 25
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 26
Plate Boundaries Three Main Boundary Types Divergent Convergent Transform 27
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 28
Convergent Plate Boundaries Types Oceanic-oceanic Subductionzone Deep oceanic trench Island arc Continental-continental High, jagged mountain chain Continental-oceanic Subductionzone Deep oceanic trench Coastal mountain range 29
Transform Plate Boundary Two plates move past each other NOT smooth Earthquakes as a result of movement 30
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 31
Another Look at Volcanoes and Earthquakes Plates and Volcanism Divergent Plate Boundaries Convergent Plate Boundaries Subductionzones Hotspots Source stationary, plates move Chain of volcanoes Earthquakes At plate boundaries or elsewhere 32
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 33
Seismology: Exploring Earth s Interior with Earthquakes 34
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 35
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 36
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 37
iclicker Question Which type of plates are on average 35km thick and made of lowerdensity rocks such as granite? A oceanic B continental C mountain 38
iclicker Question What causes tectonic plates to move: A solar energy B oceanic wave and tidal motion C mantle convection 39
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 40
iclicker Question Rocks formed when molten material cools and solidifies are called A B C D E igneous rocks sedimentary rocks metamorphic rocks fault rocks scarp rocks 41
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 commit suicide E none of the above, take other action 42