Plate Tectonics

1800s:
Discovery of undersea mountains
H.M.S. Challenger Expedition (1872-1876) with C. Darwin

1914:
Alfred Wegener (meteorologist) published "The origin of continents and oceans"

Proposed:
Theory of Continental Drift
  • opposed by geologists
  • welcomed by biologists and paleontologists
  • proposed Pangea (based on flora, fauna, shapes, rock)
  • sparked debate until the mid 1950s among continental geologists. Few looked at the oceans for answers.


    • R. Field (Princeton professor in the late 1940s)

    Sought to redefine the field of geology
    recruited a number of graduate students


    In conjunction with the war effort during World War II (big $$$) and an interest in the ocean sciences (German U-boats):
    Marine Geology and Geophysics were born

    1950s-1960s:

    Echo Sounder: identified the mid-ocean ridges
    WWSSN: World Wide Seismic Network located earthquake epicenters
    Heat flow measurements: active spreading centers
    Rock samples: basalts made up most of the oceans

     

    Harry Hess

    focused on subduction zones
    proposed convecting currents
    1962: "sea-floor spreading"


    1963: Vine and Matthews (two graduate students) explained the stripes seen on the sea-floor.

    Stripes explained as owing to sea-floor spreading of normal and reversed polarity crust.  A Canadian scientist, Morley, also proposed the same idea at the same time, but his paper was rejected as being too speculative!


    Evidence for Plate Tectonics

    1. shape of the continents
    2. square root of t, time, depth curve of the oceanic sea-floor
    3. magnetic anomalies
    4. rock/fossil assemblages
    5. age of sea-floor sediments
    6. distribution of earthquakes
    7. distribution of surface deformation
    8. direct observation (GPS)

    Back to the Class Schedule

    Please direct comments about this page to John Stimac
    URL http://www.ux1.eiu.edu/~cfjps/1300/lecture2.html
    Revised 9/5/99
    ©1999 Eastern Illinois University