Continental Drift

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Continental Drift
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Continental Drift Theory

• Proposed by Alfred Wegener in 1912
• 250 million years ago, all of the continents were
  combined into one super-continent called
  Pangaea

The continents gradually drifted apart to where
they are today.
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Plate Tectonics

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Earths Major Plates

• Eurasian Caribbean
• Australian-Indian South American
• Pacific African
• Juan de Fuca Antarctic North American

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Earths Major Plates
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2 TYPES OF CRUST
1) OCEANIC - under ocean - thin -
very dense
2) CONTINENTAL - less dense
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Theory of Plate Tectonics

• Movement leads to the formation of volcanoes,
  earthquakes, ocean trenches, mountain formations,
  etc.
• Plates move 1-10 cm per year

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• New Technology Supports Continental Drift Theory

Earthquakes and volcanoes occur in concentrated
areas. This suggests that the crust is divided
into pieces.
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In about the late 1940s, Sonar was invented.
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Bats use it!
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Sonar brought Wegners theory back to life!
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Sonar made it possible for us to observe the
ocean floor.
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Soon, scientists observed a large mountain chain
running down the center of the Atlantic ocean.
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They quickly found that the ridge ran around the
world!
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Sea- floor Spreading

• The longest chain of mountains in the world is
  the Mid-Ocean Ridge.
• The mid-ocean ridge extends into all of Earths
  oceans.

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Sea- floor Spreading

• At this ridge, the molten material rises from the
  mantle and erupts (much like a volcano).
• Molten material spreads out, pushing older rock
  to both sides of the ridge.

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Sea Floor Spreading-
Makes the mid ocean ridge.
Animation
http//www.wwnorton.com/college/geo/egeo2/content/
animations/2_1.htm
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Evidence - Drilling Samples

• The Glomar Challenger did a drilling sample and
  found rocks that are farther away from the ridge
  are the older of the rocks. The younger ones were
  in the center of the ridge.

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The further from the Mid Ocean Ridge the rocks
are, the older they are newer rocks in center
of ridge
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What causes the plates to move?
Convection currents in the mantle. Scientists
generally agree that convection occurring in the
mantle is the basic driving force for plate
movement.
Utube
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Animation
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DIVERGENT PLATE BOUNDRY

• 2 plates move AWAY from each other
• Forms volcanoes (mid-ocean ridge), cause of
  seafloor spreading and rift valleys.

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DIVERGENT PLATE BOUNDRY

• 2 plates move AWAY from each other
• Forms volcanoes (mid-ocean ridge), cause of
  seafloor spreading and rift valleys.

Sea floor spreading
Rift valley
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If new crust is being added to Earths surface,
is Earth getting bigger?
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CONVERGENT PLATE BOUNDRYS

• 2 plates move toward each other (COLLIDING)
• Three things can happen depending on what type of
  crust is colliding.
• Oceanic to Continental (Subduction)
• Continental to Continental
• (Mountains Form)
• 3. Oceanic to Oceanic
• (Subduction)

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Continental-Continental

• Crust on continents have the same density, so
  they push against each other forming mountains.
• EX Himalayan mountain range

http//www2.nature.nps.gov/GEOLOGY/usgsnps/pltec/c
ontvscont289x153.gif
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Continental/Continental Convergence
Found- India (Mt. Everest)
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Continental-Ocean

• More dense crust of ocean is pulled beneath
  (subducted) the less dense continental crust.
• Forms trench in ocean
• Forms volcanoes on land

Subduction zone
animation
http//www2.nature.nps.gov/GEOLOGY/usgsnps/pltec/c
ontvsocn288x157.gif
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What is subduction?

• Subduction is the process by which the ocean
  floor sinks beneath the continental crust and
  back into the mantle.
• Seen in the US on the Pacific Coast.

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The Ring of Fire has over 400 volcanoes , both
active and dormant. Most of the worlds
earthquakes also occur around this Ring of
Fire.
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Oceanic/Oceanic Convergence
Found- Alaska (Aleutian Islands)
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TRANSFORM

• 2 plates SLIDING HORIZONTALLY past each other
• Forms earthquakes

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Transform plates sliding horizontally past each
other.
Found- California (San Andreas Fault) Produces
earthquakes!!
All plates
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Hawaiian Islands
How they are formed In action
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Tsunami
How they are formed
Japan 2011