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Plate Tectonics Notes

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  • I have solved the problems around Alfred Wegener`s theory who have been discussed since 1911.

    22 August 1998, Jeff Hecht wrote an article in New Scientist who proves that AlfredWegeners Theory is wrong. Here is this article:

    “Magnetic shift By Jeff Hecht

    TRACES of the earth’s magnetic field frozen in rocks are yielding surprises about the planet’s past. A re-analysis of old measurements of these fields has forced geologists to conclude that either the migrating continents were clustered closer to the equator than previously thought, or that the Earth’s magnetic field was not the simple pair of poles it is today.

    Geologists track the history of continental motion by measuring the magnetism of ancient rocks. As some rocks form, they retain an imprint of the Earth’s magnetic field.

    The field direction and the age of the rock together show the latitude of the continent at the time the rock formed, provided that the shape of the terrestrial magnetic field at the time can be worked out.

    Today, the Earth’s magnetic field lines, which emanate from the poles and surround the planet, have a simple and predictable distribution.

    Geologists have proved that for at least five million years the field has been a dipole, like a bar magnet with poles aligned on the planet’s axis. And they calculate ancient latitudes assuming the field has always been a dipole, says Dennis Kent of the Lamont-Doherty Earth Observatory in Palisades, New York.

    But now Kent and Mark Smethurst of the Geological Survey of Norway in Trondheim have analysed palaeomagnetic data from rocks up to 3·5 billion years old. Instead of the magnetic distribution expected from a dipole, they found an excess of rocks from older eras with low-angle fields, as if they had formed at lower latitudes than those predicted by standard models that assume a random distribution of the early continents (Earth and Planetary Science Letters, vol 160, p 391).

    ’The surprising result is that in the Palaeozoic and Precambrian, the distributions differ markedly,’ Kent says. One possible explanation is that the Earth’s magnetic field has not always been a dipole. Kent calculates that if the ancient Earth contained elements of between four and eight poles, its magnetic field lines would have met the migrating continents at lower angles than the lines of the modern dipole field.

    That would account for the distribution he and Smethurst observed, he says. Such an arrangement might have been possible before the solid part of the core--which started growing as late as a billion years ago--reached its present size.

    The other possible explanation for the findings, Kent says, is that the continents were once clustered near the equator. Such clustering could be the result of centrifugal force tilting heavy parts of the outer layers of the Earth away from the poles (’ Twist of fate ’, New Scientist, 2 August 1997, p 15).

    Gary Glatzmaier of the Los Alamos National Laboratory in New Mexico says his unpublished simulations of the Earth’s magnetic field may be able to discover which explanation is right. According to his models, multiple poles are unlikely, he says. ’When the inner core was smaller, our simulations suggest the dipole was even stronger than today.’ If correct, Glatzmaier’s results would mean that geologists have to redraw their maps of the ancient continents.”

    From New Scientist, 22 August 1998 Proof should, as the article shows, make the geologists want to re-evaluate the foundations they build their authority upon. Particularly because this earlier model is being taught in Universities and Schools.

    In my estimation, we have a responsibility that we can not neglect when it comes to correct research theories that obviously do not hold good. Even though this is only a theory, we must be willing to re-evaluate old theories when new scientific elements come to light that prove that the former theory no longer holds good.

    Unfortunately, the tendency is that man will reject new thinking, when after a while one has built his whole research upon this one special model. In hopes that my private theory might result in an intelligent discussion, I hereby would like to present my work.

    Each individual reader is encouraged and invited to judge the results for themselves. Good luck!! Take a look at my home page where I have studied the issue for over 20 years.

    You find my work here:
    http://aspevik.webs.com/ Helge Aspevik
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  • i think this is really good , but u should also add exam style question after the slide show
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    Plate Tectonics Notes Plate Tectonics Notes Presentation Transcript

    • Plate Tectonics Earth’s Structure by Brainpop Geological Changes—3:25
    • Looking at the world map, what do you notice about the shape of the continents? Jot down your ideas on your paper…
    • The thing is…the world didn’t always look like this! It used to look like this:
    • How is this possible?!?!?
      • The lithosphere is divided into a number of large and small plates and the plates are floating on the mantle
      Plate Tectonics Theory
      • Lithosphere = the Earth’s crust plus the upper portion of the mantle layer
    •  
    •  
    •  
    • Plate motion based on The Global Positioning System (GPS)
    •  
    • Plate Boundaries
        • Divergent boundary:
        • Plates are moving away from each other
        • Midocean ridges are created and new ocean floor plates are created
    • Plate Boundaries
        • Divergent boundary:
    • Leif the Lucky Bridge Bridge between continents in Reykjanes peninsula, southwest Iceland across the Alfagja rift valley, the boundary of the Eurasian and North American continental tectonic plates.
        • Convergent Boundary : plates are moving toward each other and are colliding (3 types)
          • Create subduction zones , trenches
          • Create near coast volcanoes
          • Benioff shear zones (a pattern of earthquakes as an ocean plate grinds down the underneath side of a continent)
      When Ocean Plates collide with Contintental Plates
    • Benioff Shear Zones
    •  
    • When ocean plates collide with other ocean plates
          • Island arcs are created
          • (a pattern of volcanic islands created from a subduction zone that is located off the coast)
    •  
    •  
          • Mountain ranges are created
          • ( example : Himalayan Mountains)
      When a continental plate collides with another continental plate
    • Himalayan Mountains Mountains 2:46
    • Transform Fault Boundary
        • Plates are neither moving toward nor away from each other, they are moving past one another .
    • Transform Fault Boundary
        • The plates may move in opposite directions or in the same directions but at different rates and frequent earthquakes are created (example: San Andreas Fault)
    • San Andreas Fault
      • No
      • Plates are destroyed as fast as they are created (2 ways)
      • Plates may be subducted and melted or may push be pushed upward to form mountains
      So is the Earth getting bigger?
    • Boundaries Between Tectonic Plates—1:23
    • How can Oreos model the plate boundaries?
      • Very carefully, take just the top cookie off the Oreo.
      • Break the top cookie into 2 equal halves.
      • Replace the cookie halves back on the Oreo
      • Using the cookie,
      • Demonstrate a transform fault boundary
      • Demonstrate a divergent plate boundary
      • Demonstrate a convergent plate boundary
    •  
    • So how do the continents move?
      • Seafloor Spreading Theory :
      • Ocean floors are moving like broad conveyor belts
      • New ocean floor crust is being created at the midocean ridges
      • Convection currents within the mantle
        • The up-welling leg of the current creates a divergent boundary which produces midocean ridges
      What causes this?
    • Convection Current Demo
        • The down-welling leg of the current creates one type of convergent boundary that results in trenches and a subduction zone
      • Midocean ridges are warmer than surrounding ocean floors
      • Active volcanoes on ridges, earthquakes on ridges
      • Midocean ridge rocks are younger than surrounding ocean floor rocks
      • Midocean ridge volcanoes are younger than volcanoes further away
      What evidence do we have to support this idea?
      • Ocean floor sediments are thin on the ridges and get thicker as the distance from the ridges increase
      • Polar reversal magnetism proves that the ocean floor is moving away from the ridges
      What evidence do we have to support this idea?
    •  
    • Polar Reversal Magnetism Magnetic Poles Magnetic Field Reversals—2:54
      • Atlantic Ocean – 2-3 cm/year
      • South Pacific Ocean – 15-18 cm/year
      Speed of Spreading
      • The Seafloor is Spreading Clip—4:01
      • How Earth’s Structure Affects Plate Tectonics—5:43
      Seafloor Spreading
      • The continents have shifted their position over geologic time
      Continental Drift Theory
      • At one time all land masses were connected into one piece called Pangaea
      Continental Drift Theory 3—2:21
      • Pangaea began to split apart 200 million years ago
      • Diagram
      • North America
      • Laurasia Greenland
        • Eurasia
      • Pangaea
      • Africa
      • West G. S.America
      • Gondwanaland
      • Antarctica
      • East G. Australia
      • India
      Pangaea—A History of the Continents: 2:23
    • The First Continents 4:57
    • USGS Plate Motions Clip
        • The continents are like packages on the seafloor conveyor belt
      Continents
    •  
        • High percentage fit of continents at the 500 fathom level
      Evidence
        • Minerals, fossils, and mountains on now different continents match if the continents were together
      Evidence The Mystery of Brachiosaurus (~3 min)
    •  
        • Glaciation patterns indicate a common ice cap at the South Pole
      Evidence
        • Paleomagnetism (magnetism of old rocks) indicate a common pole if the continents were all connected
      Evidence
    •  
    • Plate Tectonics 2 –4:22
    • Plate Tectonics by Brainpop