Wegener's Continental Drift Hypothesis

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					        Wegener’s Continental Drift
              Hypothesis
      The continents fit together like a puzzle
                 Fossil Evidence
•Evidence of organisms on continents separated by
large oceans, these organisms could not swim
across the oceans
                 Geologic Evidence
•Mountain ranges of similar rock types and structure
that extend from one continent
                 Climate Evidence
Glacial evidence in areas that are now tropical
indicate continents were once located in southern
regions
Wegener’s Biggest Problem.
        Explaining HOW the
         continents move.

 Plate tectonic theory states that
the earth’s outer shell consists of
 individual plates that move and
     interact with each other
     Plate Tectonic Theory
Advances in technology provided evidence
 that plates are moving and led Geologist
    Harry Hess to develop the idea of:
   Sea floor spreading- new crust is
being created at mid-ocean ridges and
         recycled at trenches.
   Plate Tectonic Theory
          Evidence

       1. SONAR

Sonar means SOund NAvigation
          Ranging
During WWII, SONAR was used to detect
        enemy submarines.
Soundings done over the years.
  Geologists analyzed the sonar data from
               WWII and…




…discovered ridges (mountains) and trenches
(deepest parts of the ocean) on the ocean
floor. These features are directly related to
sea floor spreading and plate movement
       Sonar proved that the ocean
           floor was not flat:

 Later technological advances showed that
  these features are related to ocean floor
                 recycling.
Example: Pacific Ocean is getting smaller at
                 trenches
 Atlantic Ocean is getting bigger at ridges
    2. Magnetometers

Magnetometers were used during
WWII to detect enemy submarines.
 Scientists
  already
knew about
  Earth’s
 Magnetic
   Field
            They also
            knew that
             when Fe-
            rich rocks
             cool the
           atoms align
               in the
           direction of
              earth’s
             magnetic
  Iron          field.      Iron
atoms in                  atoms in
 magma                      rock
  In the 1960’s it was
     discovered that
   throughout earth’s
history there have been
    periods of normal
  polarity and reverse
         polarity.
   A record of these
reversals was recorded
  as the new material
along a ridge solidified
into rock on the ocean
          floor
      1960’s: Geologists analyzed the
      magnetometer data from WWII...




  …and it revealed a symmetrical pattern of
stripes on each side of the ridge representing
   the record of Earth’s magnetic reversals.
 As new material is being formed at the
ridge, the direction of the magnetic field
   is recorded as the magma hardens:
  The magnetometer evidence:
• The data showed that the magnetic fields were
  parallel to the ridge and a mirror image across
  the ridge

• This supports the theory that new material is
  being formed at the ridge and the magnetic field
  direction is being recorded over time as the
  magma hardens in to rock
         3. Radiometric dating:
Scientists collected samples of the ocean floor
crust across the Atlantic Ocean to determine
the age of these rocks
     The Glomar Challenger
It was found that the oldest rocks are located
farthest from the ridge….
and the youngest rocks are located near the
ridge….
         Radiometric dating

• The age of the rocks across the ridge
 supports sea floor spreading and plate
 tectonics by verifying that the youngest
 rocks are nearest the ridge and the oldest
 rocks are furthest from the ridge
4. GPS- Global Positioning System
• The system uses satellites to provide precise
locations of ground receivers all over the
globe
• GPS provided the first direct evidence
that continents actually move

We’ll plot GPS data on our plate maps at the end of this
unit…….