Transcript Plate Tectonics

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.”
Theory but no evidence
• Most scientist thought it was more coincidence than
fact that the landmasses appear to “fit together.”
• Couldn’t fathom a process where these large
landmasses moved, and they didn’t have any
“evidence” that they had actually moved.
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)
Pangaea
• Alfred Wegener proposed the theory of
continental drift in early 1900’s
• Wegener’s theorized that all the continents
were once a single landmass. (Pangaea)
• All continents were once joined and began
gradually moving apart, in fact they’re still
moving.
220 million years ago
Wegner’s theorized that all the continents
were once a single landmass.
• 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
• 1 Shape
• 2 -Fossil remains (Animals and Plants)
Land from the South, moving North
• 3 sea floor depth –WWII SONAR
• 4 magnetic stripes
• 5- Global Seismicity
• 6- Mountains -
Mountain formations were once connected
Review of Plate Tectonics
• What drives Earth processes?
– gravity and density differences
– external (e.g. hydrologic cycle, erosion)
– internal (e.g. mantle convection)
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)
Transform Faults
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)
...to Plate Tectonics
A. What are the lines of evidence
Wegener used to support Continental
Drift?
B. What is seafloor spreading? How do
transform faults behave oddly at the
Mid-Ocean Ridge?
C. What was the key development that
led to our current theory of Plate
Tectonics?