Plate Tectonics

1
Plate Tectonics

• Sir Francis Bacon 1620
• It appears that South America and Africa fit
  together
• Antonio Snyder published a sketch in 1655 showing
  S.A. and Africa together
• Benjamin Franklin in 1782 said
• The crust of the Earth must be a shell floating
  on a fluid interior. Thus, the surface of the
  globe would be capable of being broken and
  disordered by the violent movements of the fluids
  on which it rested.

2
Theory but no evidence

• Most scientist thought it was more coincidence
  than fact that the landmasses appear to fit
  together.
• Couldnt fathom a process where these large
  landmasses moved, and they didnt have any
  evidence that they had actually moved.

3
Drifting Continents?

1. first conception of the revolutionary theory of
   plate tectonics supported by evidence was
   proposed by the German geophysicist-meteorologist
   Alfred Wegener (1880-1930)

4
Pangaea

• Alfred Wegener proposed the theory of continental
  drift in early 1900s
• Wegeners theorized that all the continents were
  once a single landmass. (Pangaea)
• All continents were once joined and began
  gradually moving apart, in fact theyre still
  moving.

5
220 million years ago
6
Wegners theorized that all the continents were
once a single landmass.
7

• What was the Evidence and where did it come from?
• 1- Continental shape
• 2- Fossil remains
• 3- Sea Floor Depth (Global Bathymetry- SONAR)
• 4- Magnetic Stripes A geomagnetic reversal is a
  change in the Earth's magnetic field such that
  the positions of magnetic north and magnetic
  south are interchanged. The Earth's field has
  alternated between periods of normal polarity, in
  which the direction of the field was the same as
  the present direction, and reverse polarity, in
  which the field was in the opposite direction.
• 5- Global Seismic (tracking Earthquakes)
• 6 - Mountain Soil Comparison

8

• 1 Shape

9

• 2 -Fossil remains (Animals and Plants)

10
Land from the South, moving North
11
(No Transcript)
12

• 3 sea floor depth WWII SONAR

13

• 4 magnetic stripes

14

• 5- Global Seismicity

15

• 6- Mountains -

16
Mountain formations were once connected
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
Review of Plate Tectonics

• What drives Earth processes?
• gravity and density differences
• external (e.g. hydrologic cycle, erosion)
• internal (e.g. mantle convection)

21
Plate Boundaries

• divergent (e.g. mid-Atlantic ridge)
• transform (e.g. San Andreas fault zone)
• convergent
• ocean-ocean (e.g. Pacific-Pacific near Marianas
  Islands)
• ocean-continent (e.g. Pacific-North America)
• continent-continent (e.g. India-Asia)

22
(No Transcript)
23
Transform Faults
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
Review

• Plate Boundaries
• divergent (AKA constructive)
• transform
• convergent (AKA destructive)
• ocean-ocean (e.g. Mariana Islands)
• ocean-continent (e.g. Pacific-North America)
• continent-continent (e.g. India-Asia)

28
...to Plate Tectonics

1. What are the lines of evidence Wegener used to
   support Continental Drift?
2. What is seafloor spreading? How do transform
   faults behave oddly at the Mid-Ocean Ridge?
3. What was the key development that led to our
   current theory of Plate Tectonics?