Notes
Courtesy of your kind & intelligent
teacher, Mr. Whallen
Section 4.1
Alfred Wegener born 1880 Germany
proposed continents were once together.
He Said:
• 250million years ago (Mesozoic Era) Pangaea
began breaking up & continents drifted to
current locations. He Gave this a name…
Continental Drift
• Which is the apparent movement of
the continents relative to one
another over the Earth’s crust.
He did research to come up with
PROOF for this!
• A. 1st evidence: Fit of the continents.
– He cut out and pieced together a crude map
– He called the great ocean Panthalassa (meaning
all seas)
• The continent was called Pangaea (meaning
all lands)
• Continental drift animation
B. 2nd body of evidence: Matching
rocks:
Found on the following continents.
1. North Eastern N. America & Western
Europe.
2. Southern N. America & North Africa.
3. South America & Africa.
4. Not enough proof!!
C. (3rd body of evidence) Identical fossils
found all over the world:
• 1. East South America & West Africa.
• 2. Southern North America & Northern Africa.
• 3. Northern North America and Europe.
D.
th
4
evidence Climate
• 1. He found tropical fern fossils in
Antarctica.
• 2. Found many fossils in climates
opposite to what they would have lived.
• SO… He began to develop . . .
Plate Tectonics
• Study of, the formation and movement of
rigid crustal plates across the surface of the
Earth. (this movement driven by . . . )
• He never found out, died on trek to
Greenland in 1930.
Later in
the 1960s
and 70s
Plate Tectonics Truly
Developed
Scientists discovered
Convection currents – movement of partly
molten rock in the Asthenosphere, driven
by, heated, rising material from mantle.
The currents put friction on overlying
layers of crust & cause plates to move.
Plate Boundaries Divergent
Divergent Boundary
Divergent Boundary– where 2 plates are pulled
apart. In this picture 2 ocean crusts.
• Here hot less dense magma rises up through the
asthenosphere toward surface, causing the
convection currents, & undersea EQs
• MID-OCEAN RIDGE -string of undersea
divergent boundaries where new ocean crust is
formed.
• Called spreading centers & are associated with
mountainous areas on ocean floor
Plate Boundaries Convergent
Plate Boundaries Convergent
• Where 2 plates collide by moving together.
• SUBDUCTION ZONE area where an ocean plate
dives or sinks under another ocean plate, or
continental plate.
• Old crust is subducted and destroyed here.
• Dives into the Asthenosphere, melts then rises and
circulates again.
• Volcanic islands & trenches are the most common
landforms. EQ of all depths occurs.
• This is 2 Ocean crusts.
Plate Boundaries Convergent
Plate Boundaries Convergent
• This is an oceanic and continental plate subduction
zone.
• The plates move toward each other.
• Volcanoes & trenches are most common
landforms.
• Magma is generated at all subduction zones where
dense oceanic plates are pushed under lighter
continental plates, melted, and rises back up
through the crust.
• Shallow, intermediate and deep EQ occur
Plate Boundaries Convergent
Plate Boundaries Convergent
• This convergent boundary is where 2
continental crusts collide.
• The rock layers are folded and bent forming
mountains.
• The plates move toward each other.
• Mountains and Valleys are the common
land forms
Plate Boundaries Transform
Plate Boundaries Transform
• This boundary is a lateral boundary where two
plates slide past each other.
• Earthquakes occur frequently at these
boundaries.
• The plates can move in same direction but at
different rates.
• Many rolling hills and shallow trenches are
common.
• ANY TYPE OF CRUST can have be transform,
its most common on earth.
Causes of Plate Motion
1. Convection – is why plates move,
grow, get subducted.
– It is the transfer of heat energy from
inside (e) to surface. Hot less dense
rock material rises while cool more
dense rock material sinks.
Causes of Plate Motion
• 2. This convection movement pulls
plates along breaking &bending them.
– Causes magma to rise to surface at pulled
apart locations called ridges.
• 3. This makes new ocean crust.
• 4. At same time old crust is being
subducted and melted at subduction
zones.
Growth and Change Continents
• Two ways continents grow
– Microplate Terranes
– Volcanic Eruptions
• Microplate Terranes- Section of crust
formed elsewhere then scraped off
ocean crust as plate gets subducted
Each Terrane has 3 characteristics:
– 1. Contains rock & fossils different from
surrounding rock.
– 2. 3 major faults at boundaries of terrane
– 3. Magnetic properties of terrane do not
match surrounding areas.
• *California has 10 in the San Francisco
Bay area
This Has Been A Mr. Whallen
Production
•