THE CHANGING EARTH
Deep History Roots of Modern Distributions

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Geological Time Scale [+]
  • Deep History of Earth
    • Atmospheric History [+]
    • Extinctions [+]
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Geological Time Scale

  • Based on Index (guide) Fossils
    • Paleozoic Age of Fishes (570 - 248 Ma)
      • (first hard fossils) extinct trilobites
    • Mesozoic Age of Reptiles (248 - 65 Ma)
    • Cenozoic Age of Mammals (65 - 0 Ma)
    • Subdivisions of Geologic Time Scale [.]
      • eons eras periods epochs
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Geological Time Scale

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Theory of Continental Drift

  • Continental Drift: Movement of rigid continental crust over plastic asthenosphere
  • Plate Tectonics: geophysical processes producing and destroying oceanic crust
  • Basic Observation: Fit of continental margins (Snider-Pelligrine, 1858)
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Alfred L. Wegener

  • Primary Observation: fit of continental margins
  • 1915 Book
    • Geology: trans-Atlantic alignment of mountains, alignment of rock strata
    • Geophysics: change in elevation implies crustal plasticity
    • Paleontology: Glosopteris flora distribution in S. Hemisphere
    • Paleoclimatology: tropical coal beds in Northern Europe, tillites in tropical Africa
    • Biogeography: marsupials and Nothofagus in South America and Australia
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Alfred L. Wegener

  • 1929 Book (revision)
    • Match of continental margins (as in 1915 book)
    • Crust: Continental (felsic) rocks vs. oceanic (mafic) rocks
    • Proposed Tertiary Breakup of Pangea & Laurasia (no)
    • Breakup began at midocean ridge,
      spreading causes earthquakes (~)
    • Rates of movement 30-360 cm/yr (no)
    • Geothermal heat causes motion (~)
      died Nov. 1930
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Scientific Opposition to Continental Drift

  • Unsubstantiated assumptions (not proof)
    • Alternative explanations for paleontological patterns
  • Errors in Fact
    • Continent movement rates too fast
    • Earth much older than Wegener believed
  • Geological and paleontological data too scanty for rigorous test
  • No Geophysical Mechanism to force the continents to move
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Twentieth Century Evidence for Continental Drift

  • Marine Geography: better maps
    • Continental Margins show closer match than do shorelines (Bullard et al. 1965)
  • Better Stratigraphic Evidence
    • Precambrian Shield rocks match (Hurley and Rand, 1969)
    • Flood basalts match (Storey 1995)
    • Similar stratigraphic sequences (Allard & Hurst 1969)
      • Radiometric dates volcanic rocks associated with
        tillites, coal beds, and sand dunes
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Twentieth Century Evidence for Continental Drift

  • More Detailed Paleoclimatic evidence
    • extent & flow of Permian glaciers (Windley, 1977)



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Twentieth Century Paleontological evidence

  • Glossopteris (Permian plant) distribution matches across "fits." It was seasonal tree equatorward of continental ice (Schopf 1976).
  • Lystrosaurus in Antarctica, Africa, and S. India (Elliott, 1970)
  • More Biogeographic Evidence
    • Carabidae Beetle Family
    • Galaxiidea Fish Superfamily (freshwater)
    • Proteaceae Plant Family
    • Pipidae Frog Family
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  • Twentieth Century Evidence for Continental Drift

    • Better Marine Geography from Sonar Data (electronics), seafloor cores, maps







      Age: Sea floors are young

      Composition: Sea floors composed of lava (basalt)

      Ocean trenches
      Ocean Ridges

    • Guyots
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    Marine Geography and Geophysics
    The hypothesis of Seafloor Spreading [.]

    • Geological theory to explain new marine information
    • The Ocean Floor is created at the mid-ocean ridge and subducted into the ocean trenches.
      • Midocean ridges (spreading centers)
      • Ocean trenches (oceanic plate subduction zones)
      • Island arcs (oceanic plate margins).
      • Guyots (cooling and increased density with age)
      • Age (ocean floors constantly created & subducted)
      • Composition (being created by volcanism)
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    Confirmation of Seafloor Spreading

    • Earth's magnetic field varies with time
      Rock Remnant Magnetism records magnetic field
      • thermoremnant magnetism - Curie Point
      • depositional remnant magnetism
    • sensitive electronic instruments can detect remnant magnetism (Blackett 1950)
      • basalt at center normally magnetized
      • on either side, older rock with reverse magnetic polarity
      • symmetrical alternating normal - reversed stripes
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    The Current Model
    (Hess, 1962; Deitz, 1961; Vine and Matthews, 1963)
    • Earth's crust consists of two types of rocks
      • thick buoyant continental plates
      • thin dense oceanic plates
    • Oceanic crust is formed at midocean ridge
    • It spreads laterally, cooling and sinking
    • Oceanic crust is subducted beneath lighter plates
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    The Current Model

    • Three Forces Driving Plate Tectonics USGS
      • Ridge Push
      • Mantle Convection
      • Slab Pull
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    The Current Model Types of Plate Boundaries
    1. Passive Margin (N. American Atlantic Coast)
    2. Active Margins
      • Divergent Plate Boundaries
        • Midocean ridges (formation of oceanic plates)
        • Rift Valleys (Gulf of California, Rio Grande Valley, Red Sea, East Africa)
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    The Current Model Types of Plate Boundaries
    • Convergent Plate Boundaries
      • Ocean-Continent Boundaries
        • oceanic plate subducted (more dense)
        • ocean trench formed
        • coastal mountains formed (e.g., Andes) Odsen
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    The Current Model Types of Plate Boundaries
    • Convergent Plate Boundaries
      • Continent-Continent Boundaries
        • neither plate subducted
        • mountain building by compressional tectonics
          (Alp-Himalayan Mts.)
      • Crust fragments accreted to continents (terranes) () ()
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    The Current Model Types of Plate Boundaries
    • Convergent Plate Boundaries
      • Ocean-Ocean collision
        • oldest (coldest, densest) plate subducted
        • ocean trench formed
        • island arc formed (e.g., Aleutians)
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    Earth's Tectonic History Pangea
    • Gondwana
      • unified from Precambrian (650 Ma) - Ordovician (475 Ma)
      • Southern Hemisphere fragments: (today's Southern Hemisphere)
      • Northern Hemisphere fragments: Arabia and India
    • Laurasia
    • Gondwana & Laurasia collide during Carboniferous (306 Ma)
    • Asia collides with Laurasia in Permian (270 Ma) (forms Urals)
      • all land masses connected (Pangea)
      • no divisions of ocean (Pantalassia)

    Maps are from [Scotese] Web doGS next






    Earth's Tectonic History

    • Breakup of Pangea Triassic
      • rifting between Asia and North America forms Turgai Sea Jurassic (180 Ma)
      • rifting between North America and Europe Cretaceous (100 Ma)
    • Breakup of Laurasia
      • rifting between Pangea and Laurasia opens circum-equatorial sea (Tethys) (100 Ma)
      • Beringia connects Asia and North America - produces "Holarctic" biota

    Maps are from [Scotese] Web doGS next






    Earth's Tectonic History

    • Breakup of Gondwana [diagram]
      • rifting between eastern (Africa & S.A.) and western Pangea Jurassic (180 Ma)
      • rifting between Africa and South America Jurassic (160 Ma)
      • rifting between Madagascar-India and Antarctica-Australia Jurassic (130 Ma)
      • rifting between Antarctica and Australia Cretaceous (100 Ma)
      • rifting between Madagascar and India [Pliocene] (90 Ma)
      • collision of India with Asia Eocene/Oligocene (40-36 Ma *)

    *Najman et al. 2001. Nature 410: 194.
    Maps are from [Scotese] Web doGS next






    Earth's Tectonic History

    • Formation of Central America and the Antilles [.]
      • rifting between North and South America Jurassic (150 Ma)
      • island arcs of Antilles and Central American Archipelago drift eastward (120 - 58 Ma)
      • proto Antilles form land bridge Cretaceous (65 Ma)
      • collision of oceanic plates creates Panama Land Bridge Pliocene (3.5 Ma)

    Maps are from [Scotese] Web doGS next






    Effects of Plate Tectonics

    • Cretaceous Eperic (Epicontinental) Seas
      • few continental glaciers
      • shallow seafloor (small ocean basins)
        • Australia divided into 3 small continents
        • North American divided in half
    • More biogeographic barriers for terrestrial organisms
    • Distribution corridor for aquatic organisms
    Maps are from [Scotese] Web doGS next






    Effects of Plate Tectonics

    • Mediterranean and Red Sea
      • Collision of Africa and Europe Eocene (35 Ma)
      • Closure of Gibraltar Miocene (24 Ma) salt deposits [.] (desert)
      • Rifting of Mediterranean Basin Miocene (5 Ma)
    • Barrier (terrestrial) / Corridor (marine)
    Maps are from [Scotese] Web doGS next






    Effects of Plate Tectonics

    • Oceanic Islands (Unique Biogeographic Entities)
      • Hot Spots
        • Hawaiian Island Emperor Seamount Chain [+] [+]
        • Pacific Plate moving northward into Aleutian Trench
        • Hotspot produces chain of islands
          • Hawaiian Chain 0 - 44 Ma
          • Emperor Chain 44 - 80 Ma
      • Triple Junctions
        • Galapagos Islands Juncture of Nazca, Cocos and S. American Plates
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    Effects of Plate Tectonics

    • Paleo Ocean Circulation
      • Tethean circum-equatorial seaway (Cretaceous)
      • Rifting of Australia and Antarctica created circum-Antarctic circulation Eocene (40 Ma)
      • Rifting of Australia and South America
      • Collision of oceanic plates creates Panama Land Bridge Pliocene (3.5 Ma)
    • Global-scale climatic and biogeographic effects
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    Climatic and Biogeographic Consequences of Plate Tectonics

    • Formation of Pangea
      • Reduced area of shores continental shelves, globally
      • Produced cold and arid continental interior
      • Prevented circum-equatorial circulation (global cooling)
      • Formed land mass at south pole (global cooling)
    • Ammonites vs. Area of Epicontinental seas (Mesozoic)
    • Decreasing similarity of coastal faunas as Atlantic opens (Fallaw 1979)
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    The Paleogeographic Atlas Project
    Latitudinal History after W.R.Dickinson, 1989 next




    Expanding Earth dot Org next