GSU GEOL 1122K - Study Guide Chapter 2 Geology Questions (17 pages)

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Study Guide Chapter 2 Geology Questions



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Study Guide Chapter 2 Geology Questions

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17
School:
Georgia State University
Course:
Geol 1122k - Introductory Geosciences Ii
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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 1 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 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 13 The Earth s Magnetic Field Geographic and magnetic poles are not the same 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 17 Polar Wandering Layered basalts record magnetic changes over time Inclination and declination indicate change in position 18 Apparent Polar Wandering Polar wandering paths were initially misinterpreted Not the signature of a wandering pole on a fixed continent The signature of a fixed pole on a wandering continent 19 Polar Wandering Each continent had a separate polar wandering path Now understood to represent that The location of the magnetic pole is fixed The continents themselves have moved These curves align when continents are reassembled 20 Sea Floor Bathymetry Before World War II we knew little about the sea floor Echo sounding sonar allowed rapid sea floor mapping Sea floor maps created by ships crossing the oceans 21 The Ocean Floor Oceanographers were surprised to discover that A mid ocean mountain range runs through every ocean Deep ocean trenches occur near volcanic island chains Submarine volcanoes poke up from the ocean floor Huge fracture zones segment the mid ocean ridge These observations are all explained by plate tectonics 22 The Ocean Floor Sonar mapping delineated bathymetric features Mid ocean ridges Deep ocean trenches Volcanic islands Seamounts Fracture zones 23 The Ocean Floor Today s view of the ocean floor reveals the location of Mid ocean ridges Deep ocean trenches Oceanic fracture zones 24 The Oceanic Crust By 1950 we had learned much about oceanic crust Oceanic crust is covered by sediment Thickest near the continents Thinnest or absent at the mid ocean ridge Oceanic crust consists primarily of basalt Lacks variety of continental rock types No metamorphic rocks Heat flow is much greater at the mid ocean ridges 25 The Oceanic Crust Earthquakes occur in distinct belts in oceanic regions The earthquakes were surprising They were limited to Parts of oceanic fracture zones Mid ocean ridge axes Deep ocean trenches Geologists realized that earthquakes defined zones of movement 26 Sea Floor Spreading In 1960 Harry Hess published his Essay in Geopoetry Sediment thickens away from ridges Earthquakes at mid ocean ridges indicate cracking Cracked crust splits apart


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