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Thursday 9/5/13 • LT: I can set reasonable goals for my grade in this class. • I can describe continental drift • BR: How do you think you did on the test yesterday? 1 Plate Tectonics is one of the most exciting recent theories in Earth Science. It began with an idea based on observations made 400 years earlier. 2 • 400 years ago, early explorers like Magellan and Columbus brought back information about new continents and their coastlines. •Cartographers charted those new discoveries and produced the first reliable world maps. 3 In 1912, Alfred Wegener, a German scientist, proposed the hypothesis of CONTINENTAL DRIFT “clearly an idea before its time” 4 1.The continents used to be a single landmass, or supercontinent called = PANGAEA [all lands] 2.This supercontinent was surrounded by a huge ocean called = PANTHALASSA [all seas] 5 6 Pangaea app. 250M yrs ago 7 3.About 250M years ago, Pangaea began to break up 4.The continents slowly drifted to their actual locations. 8 •Pangaea is not the only “super continent” that ever existed. •Rodinia is another “motherland” that formed more than 1100M years ago. •It is to be understood that the separation and coming together of landmasses always occurred, and are still happening. This is known as the: •Supercontinent Cycle. 9 Pangaea was surrounded by all seas called: A. B. C. D. Oceanographia Panthalassa Antarctica Ishoudinotha 10 The continents used to be a single landmass called: A. Hugeenaea B. Panthalassa C. Pangaea D. Americeuropa 11 Who was the first to propose the hypothesis of the Continental Drift? A. Robert Wagener B. Louis Pasteur C. Alfred Wegener D. Andrija Mohorovicic 12 EVIDENCE 1 FIT OF THE CONTINENTS Continental shorelines on either sides of the Atlantic ocean had such similarities that they looked like parts of a giant JIGSAW PUZZLE: 13 Bulge of Africa fits the shape of North America South America fits along the coast of Africa beneath the bulge Greenland seems to fit between North America and north western Europe. 14 Untold tragedies of Continental Drift. . 15 According to the “jigsaw puzzle” evidence, the bulge of the African coast fits the contour of : A. East coast of North America B. West coast of South America C. Greenland D. Europe 16 EVIDENCE 2 FOSSILS MATCH The presence of identical fossil species [animals and plants] on now widely separated coastlines support the theory that those continents were once joined. 17 LOCATION OF VARIOUS DISCOVERIES Madagascar 18 EVIDENCE 2 FOSSILS MATCH Glossopteris a fern found in Australia and Antarctica 19 Madagascar land reptile land reptile freshwater reptile 20 Permian ferns Mesosaurus, a freshwater reptile, could not have been able to swim across the Ocean, and no evidence of land bridges. 21 EVIDENCE 3 GEOLOGICAL MATCH Rock layers’ sequence [structure], age and types [basalt, sandstone], are identical on opposite sides of the Atlantic Ocean. Appalachians Mtns [North America] and mountains in Scotland and Scandinavia. 22 Matching of mountain ranges on different continents 23 When the continents are reassembled, the mountain chains form a continuous belt — having the same rock types, structures and rock ages. 24 EVIDENCE 4 PALEOCLIMATIC MATCH Scientists found glacier evidence in places that are now warm (Africa) and tropical plant fossils in areas that are now cold (Antarctica). This couldn’t be possible….. 25 EVIDENCE 4a PALEOCLIMATIC MATCH Unless: 1) the Atlantic ocean did not exist, 2) the continents were joined AND 3) they were all close together near the South Pole of Pangaea. 26 Pangaea with SAfrica centered over the South Pole accounts for glacial ice in the Southern continents 27 EVIDENCE 4b PALEOCLIMATIC MATCH Discoveries of large concentrations of fossils of tropical plants [in the form of coal deposits] in eastern US, Siberia, Antarctica suggest that they were once situated closer to the Equator, in a more tropical climate where lush, swampy vegetations could grow. 28 Now cooler climate regions that used to be at the Equator Glaciers movement centered over South Pole 29 • Despite all the evidences – Jigsaw puzzle [cartography] – Fossils [paleontology] – Geological match [geology] – Climatic patterns [paleoclimatology] • Wegener’s hypothesis was rejected because he could not explain: – What forces could move the continents – How continents could plow through the stationary ocean floor without crumbling. • He died in 1930 before finding the ultimate answer 30 What kind of fossil evidence supported Wegener’s hypothesis? A. Fossils hinting at a land bridge between South America and Africa B. Fossils proving Mesosaurus never lived in Africa C. Plant fossils showing that cold areas used to be tropical D. Sea fossils proving the continents had plowed through the ocean floor 31 Wegener speculated that over millions of years smaller landmasses A. Moved closer together B. Drifted to their present locations C. Did not move D. Drifted to the southern hemisphere 32 Seafloor Spreading: Harry Hess’s hypothesis Underneath the ocean, molten magma was coming through cracks as both sides of the tectonic plates were moving AWAY from each other. The moving ocean floor was replaced by the rising magma that cooled and solidified into new rock. 33 Harry Hess’s hypothesis ocean crust is formed at ocean ridges and destroyed at deepsea trenches. Maybe the ocean floor moving was the force responsible for the movement of the continents Thus came the idea of SEAFLOOR SPREADING 34 A REVIEW Earth’s Magnetic Field • The Earth's magnetic field produces invisible lines of force that extend from one pole to the other. • A compass needle aligns itself with these lines of force, meaning that it points toward the magnetic poles. 35 36 PALEOMAGNETISM • When igneous rocks containing magnetic minerals solidify, the crystals align themselves with the Earth's magnetic field. • The magnetic field of the rock then points toward the magnetic pole that existed when the rock formed. • If the rock is moved, its magnetic field will act as a “fossil compass”. 37 • Basalt is rich in iron-bearing materials, like magnetite. • As the basalt lava cools, the Fe-bearing minerals become oriented parallel to the Earth’s magnetic field. 38 • As the lava hardens, the magnetic orientation is preserved and provides a record of the current Earth’s magnetic field. 39 . 40 As new seafloor is created at the ridge, it is added in equal amounts to both trailing edges of the spreading seafloor. The pattern of stripes appear as mirror images on both sides of the ridge which is the strongest evidence for seafloor spreading. 41 Magnetic history of the Earth showed a symmetrical or mirror-image stripes parallel to the ocean ridges 42 43 Theory of Plate Tectonics From the hypotheses of Continental Drift and Seafloor Spreading came the Theory of Plate Tectonics 44 Theory of Plate Tectonics The Earth’s crust and rigid upper mantle are broken into huge slabs or plates. Those plates are riding/floating on the mantle [like wood blocks on water], at different rates and different directions. 45 Directions and rates of plate motions Subduction Spreading 46 The oceans and the continents are carried as passengers onto the moving plates. 47 The constant movement of those plates is responsible for the changes to the Earth’s surface by the way of: 48 EARTHQUAKES 49 V O L C A N I C E R U P T I O N S 50 MOUNTAIN RANGES 51 RIFT VALLEYS 52 Ocean basins FORMATION / DESTRUCTION 53 8 major plates: 1) 2) 3) 4) 5) 6) 7) 8) North American South American Eurasian African Pacific [largest] Indian/ Australian Antarctica Nazca The minor ones: Juan de Fuca, Cocos, Caribbean, Scotia, Arabian, Philippine 54 55 BOUNDARIES •Tectonic plates interact at places called BOUNDARIES. •The continents / oceans do not necessarily resemble the outline of the plate boundaries. •There are three types of boundaries, each one associated with specific geologic activities and/or features. 56 Divergent Boundaries Two plates moving AWAY from each other and forming a gap or RIFT. • Mostly associated with OCEANIC crust [seafloor spreading = Mid-Atlantic Ridge] – as molten rock [MAGMA] from the mantle rises the plates move apart, and fills the space between the plates. – as it cools, it hardens onto the edges of the plates and creates new crust. 57 DIVERGENT PLATES “CONSTRUCTIVE” 58 59 Divergent Boundaries • Some involve the CONTINENTAL crust – when it begins to separate, the stretched crust forms a long, narrow, depression called a RIFT VALLEY • it is currently happening between the African and Arabian plates Red Sea is therefore widening 60 DIVERGENT 61 RIFT VALLEYS 62 Mediterranean Sea 63 Convergent Boundaries Two plates moving TOWARDS each other. • Direct COLLISION of one plate with another one. • There are three POSSIBILITIES: – CONTINENTAL – OCEANIC – OCEANIC – OCEANIC – CONTINENTAL – CONTINENTAL 64 CONTINENTAL - OCEANIC • As the plates are colliding, the denser plate will be forced downwards • Since the oceanic crust is denser than the continental crust, the ocean plate is pushed under continental plate. [crust destruction] The area is called a SUBDUCTION ZONE, and forms a deep-ocean trench • As the plate sinks into the mantle, it melts and becomes magma. The magma rises through the continental plate and forms a volcanic chain 65 “DESTRUCTIVE” OCEANIC CONTINENTAL 66 Mount Hood near Portland, Oregon Cascades range 67 Mount St. Helens, Washington Cascades range 68 Volcanic mountains of the Andes, (Nazca and South American Plates) 69 TRENCH 70 71 OCEANIC – OCEANIC • The more dense of the 2 will go under and form a subduction zone / OCEAN TRENCH • The new mantle material produced from the melting of the subducted plate will eventually resurface to produce chain of volcanic islands on the ocean floor called ISLAND ARCS • As magma accumulates over time, the volcanoes may rise above sea level to form volcanic islands: Mariana trench and the Mariana Islands in the west Pacific ocean 72 OCEANIC-OCEANIC CONVERGENCE “DESTRUCTIVE” 73 74 75 76 CONVERGENT PLATES “DESTRUCTIVE” 77 CONTINENTAL - CONTINENTAL • As the 2 continental plates are colliding, neither plate is subducted i.e. neither plate goes beneath the other WHY? – because the Continental crust is too buoyant to sink into the mantle. • The colliding edges buckle and are pushed upward to form mountain ranges. Indian/Australian plate collide with the Eurasian plate to form the HIMALAYAS. 78 CONTINENTAL – CONTINENTAL CONVERGENCE 79 The collision of India and Asia produced the Himalayas (before) 80 The collision of India and Asia produced the Himalayas (after) 81 Mountain Building 82 Transform Boundaries Two plates PASSING each other. • Plates are grinding past each other and the crust is either cracked or deformed. • Motion is not smooth but rather in spurs of sudden moves generating EARTHQUAKES* • They are followed by periods of low or no activity San Andreas Fault * Earthquakes can occur / are common along all boundaries 83 TRANSFORM FAULT “CONSERVATIVE” Crust is nor created nor destroyed 84 85 Tectonic plates can include A. only asthenosphere. B. only oceanic crust C. only continental crust D. both oceanic and continental crust. Features found at divergent boundaries include ____. A. ocean ridges B. deep-sea trenches C. crumpled mountains D. island arc volcanoes Continental-continental plate collisions produce ____. A. island arcs B. rift valleys C. deep-sea trenches D. very tall mountain ranges The theory that explains why and how continents move is called A. continental drift B. paleomagnetism C. plate tectonics D. sea-floor spreading The Himalaya Mountains were formed in a collision at a A. divergent boundary B. convergent boundary C. transform boundary. D. fracture zone Crust is neither destroyed nor formed along which of the following boundaries? A. convergent B. divergent C. transform D. magnetic SUMMARY Direction of movement Type of Boundary/ impact on crust Plates involved Geological activities/ features Examples 92 Importance of plate tectonics • Theory provides an explanation of Earth’s major surface processes • Geologists have found explanations for the geologic distribution of earthquakes, volcanoes and mountains and the distributions of plants and animals fossils. #1 MATCH • DIVERGENT • CONSERVATIVE • CONVERGENT • DESTRUCTIVE • TRANSFORM • CONSTRUCTIVE What causes Plate Movement? While several models have been proposed to explain the DRIVING MECHANISM responsible for their movement, there is no doubt that the Earth’s internal heat is the DRIVING FORCE. 98 DRIVING MECHANISM Convection Currents the rising-sinking action of magma due to the heat in Earth’s core Magma close to the core is heated, It expands, lowering its density, and then rises Closer to the crust, the magma cools, it contracts, increasing its density, and then sinks due to gravity 99 Convection currents 100 101 The driving mechanism of tectonic plates movement are related to convection currents in Earth’s ____. A. crust B. mantle C. inner core D. outer core The downward part of a convection current causes a sinking force that ____. A. pulls tectonic plates toward one another B. moves plates apart from one another C. lifts and splits the lithosphere D. creates a divergent boundary Which of the following is an example of a divergent plate boundary? A. [Option 1] B. [Option 2] C. [Option 3] D. [Option 4] 104 At what type of plate boundary does sea-floor spreading occur? A. convergent oceanic-oceanic boundaries B. convergent oceanic-continental boundaries C. divergent oceanic-oceanic boundaries D. transform boundaries The force behind the movement of Earth’s plates is A. cooling of magma cells that rises to the Earth’s surface B. magnetic attraction between Earth’s iron core and its poles C. temperature differences between Earth’s oceanic and continental plates D. the Earth’s internal heat producing convection currents in the mantle.