Presentation on theme: "Plate Tectonics Chapter 17 Great Idea:"— Presentation transcript:
1 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.
2 Chapter Outline The Dynamic Earth Plate Tectonics: A Unifying View of EarthAnother Look at Volcanoes and Earthquakes
3 The Dynamic Earth Small-scale changes Large-scale changes Construction siteErosion by rainLarge-scale changesVolcanoesEarthquakesErosion
4 The Case of the Disappearing Mountains ErosionFew hundred million yearsMountains continually formingEarth’s surface is not static
5 Map of continentsA map of the world’s continents reveals the similar shapes of coastlines on the two sides of the Atlantic Ocean.
6 The Movement of the Continents F. BaconContinents like a puzzleWegenerContinental DriftContinents inmotionCurrent EvidenceOcean FloorsMagnetic ReversalsRock Ages
7 The German scientist A. Wegener ( ) postulated that a supercontinent once existed — and later broke apart — called Pangea.
8 Plate Reconstructions Once the motion of continents was determined, scientists could predict how the Earth’s surface might have looked in the past. More than 200 million years ago, the present-day continents were joined together as the ancient continent Pangaea.
12 Spreading Ridge magmatism (Iceland) Magnetic stripes that parallel ocean ridges must form as new magma wells up from the fissure and pushes out to the sides.In this cross-sectional view, older rocks lie farther from the ridge. (The “lithosphere” includes the uppermost mantle and all of the crust.)
13 Magnetism of the sea floor Measurements in the late 1950s and early 1960s revealed magnetic stripes running nearly parallel to the Vancouver province and Washington state coastlines.
14 Rock Ages Radioactive Isotopes Rocks near Mid-Atlantic Ridge younger Rocks farther away older
15 New Support for the Theory Measuring motion of continentsRadio AstronomyMeasured arrival of radio wavesRepeated over several yearsNorth America and EuropeSeparating at 5 cm per year
17 Plate Tectonics Plate Tectonics Tectonic plates Earth’s surface Large-scale surface featuresRelated phenomenaTectonic platesRigid, moving sheet of rockCrust and upper mantleContinental100 km thickLower density (granite)Oceanic8-10 km thickDense rock (basalt)Earth’s surface¼ continent, ¾ water
18 Plate motionsThe major plates of the Earth with their directions of motion shown by arrows.
19 The Convecting Mantle Mantle convection Sources of energy Movement Motion driven by Earth’s interior heat energySources of energyGravitational potential energyDecay of radioactive elementsMovementHeat moves to cooler regionsConvection cells in mantleVery slow200 million years for one cycle
20 Seafloor Spreading: In the 1960’s, Harry Hess, Robert Deitz and other geologists and oceanographers, put forward the hypothesis of ‘seafloor spreading.’ The key data for this hypothesis were the topographic maps of the ocean floors….
28 The ‘Afar triangle’A satellite photograph of a portion of Africa’s Great Rift Valley. The narrow body of water defines a divergent plate boundary where new plate material is being created and plates are moving out to either side.
29 Gulfs formed between rifted continental fragments:
35 The layers of EarthThe principal layers, which differ in chemical composition and physical properties, are the core, the mantle, the crust, and the atmosphere (not shown). When looked at in detail, each of these layers is itself composed of smaller layers.
36 Volcanoes and Earthquakes- Evidence of Earth’s Inner Forces Magma breaks through surfaceEarthquakeRocks breaks along faultEnergy transmitted as waveRichter scale
37 Volcanic settingsA cross-section of a volcano reveals a magma chamber, which stores molten rock, and a system of pipes, cracks, and vents that lead to the surface. The terms in the orange area refer to the kinds of rock formations resulting from cooled magma. Xenoliths are the original rocks encased in this cooled magma.
38 Divergent Plate Boundaries A divergent plate boundary defines a line along which new plate material is formed from volcanic rock.
40 Hawaiian example of plate motion Kauai, currently the oldest, is between 3 and 5.5 million years old, while Hawaii, the youngest, is less than 0.8 million years old.
41 Another Look at Volcanoes and Earthquakes Plates and VolcanismDivergent Plate BoundariesConvergent Plate BoundariesSubduction zonesHotspotsSource stationary, plates moveChain of volcanoesEarthquakesAt plate boundaries or elsewhere
42 Seismology: Exploring Earth’s Interior with Earthquakes Study of sound vibrations within earthUsed to determine earth’s inner structureSeismic wavesCompressional or longitudinalTransverse or shear waves
43 Seismology: Exploring Earth’s Interior with Earthquakes
44 A Clicker Question.How do we know that the Earth’s tectonic plates move (continental drift)?Observation of the Earth’s riversDirect measurements, observation of the rifts in the ocean floors, magnetic reversalsCalculations by EinsteinErosion of mountains
45 The Geological History of North America Northeastern Canada and GreenlandSeveral billion years oldWestern USTerranesAdded to continent over timeAppalachian MountainsFormed million years agoContinental-continental convergence zoneRocky Mountains60 million years agoWarping, folding and fracturing of continentThe Colorado PlateauGentle upliftThe Sierra NevadaMolten rock pushed up sediments