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PE3 - CD_SFS - Continental Drift and Sea-Floor Spreading...

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Unformatted text preview: Continental Drift and Sea-Floor Spreading Ring of Fire 1 Alfred Wegener Formulated the theory of continental drift Pangea (200 million years ago) The supercontinent Pangea – assembled at the end of the Paleozoic 2 Pangea Pangea - near the end of the Paleozoic The continents drifted apart Now Wegener’s evidence Wegener used 4 kinds of data to prove that continents moved 1. The continents fit together like a jigsaw puzzle 3 Wegener’s evidence Wegener used 4 kinds of data to prove that continents moved 2. Locations of fossils • Glossopteris • Mesosaurus Wegener’s evidence Fossil Leaf of Glossopteris 4 Wegener’s evidence Distribution of fossils Mesosaurus - aquatic reptile Wegener’s evidence 5 Wegener’s evidence Wegener used 4 kinds of data to prove that continents moved 3. Similar major rock structures of same age Wegener’s evidence Matching Mountain Chains 6 Wegener’s evidence Matching Mountain Chains Wegener’s evidence 4. Paleoclimate evidence glaciers Wegener used 4 kinds of data to prove that continents moved 7 Wegener’s evidence Other paleoclimate evidence What did other scientists think of Wegener’s idea: A. It was immediately successful and widely accepted B. Most scientist were cautiously hopeful the idea would be found correct C. Although most scientists were initially skeptical it was quickly accepted D. The idea was completely rejected 8 "Utter, damned rot!" President of the prestigious American Philosophical Society "If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again." American scientist "Anyone who values his reputation for scientific sanity would never dare support such a theory." British geologist How many magnetic north poles does Earth have: A. one B. two C. three D. four 9 Magnetic Field Dipole magnet Earth You are here Apparent polar wander W. W. Norton 10 Apparent polar wander Apparent polar wander Earth has only one magnetic north pole Earth’s magnetic poles do not move (much) W. W. Norton Magnetic poles are near the rotation poles 11 What do apparent polar wander curves tell us: A.  the oceans are much younger than was believed by earlier scientists B.  moving continents make the magnetic field appear to change position C.  Earth has had more than one magnetic north pole at times in the past D.  Earth’s magnetic poles have moved great distances through geologic time The Sea Floor Echo Sounding 12 Heezen & Tharp Heezen & Tharp made the first map of the ocean bottom Sea Floor Spreading Harry Hess Formulated the theory of Sea Floor Spreading 13 Hess data Mid Atlantic Ridge is in the center of the ocean Mid ocean ridges have lots of heat flow and tension Oceans are young because they only have 1.3 kms of sediment piled up Conduction: Conduction is the transfer of heat from a solid to another solid touching each other. Convection: The transfer of heat by circulation or movement through liquid or gases. Radiation: Radiation is the transfer of heat from an object traveling through a space until absorbed by another object. 14 Magnetic Field Nature of Earth s magnetic field W. W. Norton 15 Magnetic polarity Normal Reversed The Earth s magnetic field changes polarity from normal to reversed Magnetic polarity The last reversal, called the Brunhes-Matuyama reversal, occurred 780,000 years ago 16 Depositional Remanent Magnetism Recording the magnetic field in newly deposited sediment Iron particles in the sediment line up with the Earth s magnetic field as they settle out Thermal Remanent Magnetism As lava cools, Earth s magnetic field is preserved in iron particles in the lava W. W. Norton Curie Point - ~770oC; direction of the existing magnetic field locks in when a melt cools below this temperature 17 Sea floor polarity W. W. Norton A magnetometer towed by a ship can measure the magnetic polarity of the sea floor Magnetic anomalies The rocks at the bottom have magnetic stripes parallel to the ridge 18 Magnetic anomalies MOR Symmetry of stripes W. W. Norton Vine and Matthews explained the stripes – •  New ocean crust, made at a mid-ocean ridge, is magnetized with present day field. •  Older crust, some distance from the ridge, with reversed polarity, formed when the magnetic field was reversed. Magnetic anomalies Eltanin profiles of magnetic anomalies Magnetic anomaly, gamma Ocean depth, km The vertical scale for total intensity anomaly, DF, is shown in gammas . This is the same as nanoTeslas or nT. The horizontal lines are at zero anomaly; the scale is thus minus 500 to plus 500 nT. 19 Magnetic anomalies The incredible symmetry of the Eltanin 19 profile ESE WNW WNW mirror image of measured profile to show symmetry ESE measured profile of total intensity anomalies Magnetic anomalies are symmetrical about the spreading ridge. 20 ...
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