GSU GEOL 1122K - Study Guide Chapter 2 (14 pages)

Essentials of Geology 4th edition by Stephen Marshak 2013 W W Norton Company Chapter 2 The Way the Earth Works Plate Tectonics 1 Chapter 2 The Way The Earth Works Plate Tectonics 2 In this Chapter What were Wegener s observations Paleomagnetism the key proof of continental drift Observations that led Harry Hess to sea floor spreading Three kinds of plate boundaries Plate interactions and rates of plate movement 3 Alfred Wegener German meteorologist and polar explorer Wrote The Origins of the Continents and Oceans in 1915 He hypothesized a former supercontinent Pangaea He suggested that land masses slowly move continental drift These were based on strong evidence Fit of the continents Glacial deposits far from polar regions Paleoclimatic belts Distribution of fossils Matching geologic units 4 Plate Tectonics Wegener s idea was the basis of a scientific revolution Earth continually changes Continents move split apart and recombine Ocean basins open and close His hypothesis was met with strong resistance What force could possibly be great enough to move the immense mass of a continent PowerPoint slides prepared by Rick Oches Professor of Geology Environmental Sciences Bentley University Waltham Massachusetts 5 Plate Tectonics The scientific revolution began in 1960 Harry Hess Princeton proposed sea floor spreading As continents drift apart new ocean floor forms between Continents converge when ocean floor sinks into the 1 Ocean basins open and close His hypothesis was met with strong resistance What force could possibly be great enough to move the immense mass of a continent Essentials of Geology 4th edition by Stephen Marshak 2013 W W Norton Company Chapter 2 The Way the Earth Works Plate Tectonics 5 Plate Tectonics The scientific revolution began in 1960 Harry Hess Princeton proposed sea floor spreading As continents drift apart new ocean floor forms between Continents converge when ocean floor sinks into the interior By 1968 a complete model had been developed Continental drift sea floor spreading and subduction Earth s lithosphere is broken into 20 plates that interact 6 Glacial Evidence Evidence of Late Paleozoic glaciers found on five continents Some of this evidence is now far from the poles These glaciers could not be explained unless the continents had moved 7 Paleoclimatic Evidence Placing Pangaea over the Late Paleozoic South Pole Wegener predicted rocks defining Pangea climate belts Tropical coals Tropical reefs Subtropical deserts Subtropical evaporites Fossil Evidence Identical fossils found on widely separated land Lystrosaurus A nonswimming land dwelling reptile Cynognathus A nonswimming land dwelling mammal like reptile These organisms could not have ocean PowerPoint slides prepared by Rick crossed Oches Professoran of Geology Environmental Sciences Bentley University Waltham Massachusetts Pangaea explains the distribution 8 2 Fossil Evidence Identical fossils found on widely separated land Lystrosaurus A nonswimming land dwelling reptile Cynognathus A nonswimming land dwelling mammal like reptile Chapter 2 Essentials of Geology 4th edition The Way the Earth Works Plate Tectonics by Stephen Marshak These organisms could not 2013 W W Norton Company have crossed an ocean Pangaea explains the distribution 8 9 Matching Geologic Units Distinctive rock assemblages and mountain belts match across the Atlantic 10 Criticisms of Wegener s Ideas Wegener had multiple lines of strong evidence Yet his idea was debated ridiculed and ignored WHY He couldn t explain how or why continents moved Wegener died in 1930 on a Greenland expedition Over the next three decades new research new technology and new evidence from the oceans revived his hypothesis 11 Earth s Magnetic Field Flow in the liquid outer core creates the magnetic field It is similar to the field produced by a bar magnet The magnetic pole is tilted 11 5 from the axis of rotation geographic north 12 Magnetic Poles The magnetic pole intersects Earth s surface just like the geographic pole does Magnetic N pole and magnetic S pole both exist Magnetic poles are located near geographic poles The Earth s Magnetic Field Geographic and magnetic poles are not the same PowerPoint slides prepared Rick Oches Professor of Geologyto Environmental Sciences Waltham Massachusetts Abycompass points magnetic N Bentley notUniversity geographic N The difference between geographic N and magnetic N is called declination It depends on Absolute position of the two poles Geographic north Magnetic north 13 3 geographic pole does Magnetic N pole and magnetic S pole both exist Magnetic poles are located near geographic poles The Earth s Magnetic 13 of Geology Essentials 4th edition Field Chapter 2 The Way the Earth Works Plate Tectonics by Stephen Marshak Geographic and magnetic poles are not the same 2013 W W Norton Company A compass points to magnetic N not geographic N The difference between geographic N and magnetic N is called declination It depends on Absolute position of the two poles Geographic north Magnetic north Longitude 14 The Earth s Magnetic Field Curved field lines cause a magnetic needle to tilt Angle between magnetic field line and surface of the Earth is called inclination It depends on Latitude 15 Paleomagnetism Rock magnetism can be measured in the laboratory The study of fossil magnetism is called paleomagnetism Iron Fe minerals in rock preserve information about the magnetic field at the time the rocks formed Declination and inclination preserved in rocks often vary from present latitude longitude Instruments used in paleomagnetism record changes in position These data are used to trace continental drift 16 Paleomagnetism Iron minerals archive the magnetic signal at formation Cooled magma Low Temp permanent magnetization Thermal energy of atoms slows Dipoles align with Earth s magnetic field Magnetic dipoles become frozen in alignment with field PowerPoint slides prepared by Rick Oches Professor of Geology Environmental Sciences Bentley University Waltham Massachusetts 17 Polar Wandering Layered basalts record magnetic changes over time Inclination and declination indicate change in position 18 Apparent Polar Wandering 4 Iron minerals archive the magnetic signal at formation Cooled magma Low Temp permanent magnetization Thermal energy of atoms slows th edition align with Earth s magnetic field 4Dipoles Chapter 2 Essentials of Geology The Way the Earth Works Plate Tectonics by Stephen Marshak Magnetic dipoles become frozen in