PLATE TECTONICS Chapter 10

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PLATE TECTONICSChapter 10

• Section 3
• The Changing Continents
• (pg 255-260)

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REVIEW

• What are the 3 types of plate boundaries
• DIVERGENT BOUNDARIES
• CONVERGENT BOUNDARIES
• TRANSFORM BOUNDARIES

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• At a DIVERGENT BOUNDARY
• a RIFT VALLEY is
• A NARROW VALLEY THAT FORMS WHERE TECTONIC PLATES
  ARE SEPARATING
• A rift valley can be found running down the
  center of a ___-______ _____
• MID-OCEAN RIDGE

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• What happens at a convergent boundary?

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REVIEW

• What happens when
• Continental crust hits oceanic crust
• Continental crust hits continental crust
• Oceanic crust hits oceanic crust

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CONVERGENCE between OCEANIC CONTINENTAL
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What is the OTHER boundary?

• Transform
• What happens at transform boundaries?
• Plates slide side by side!

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REVIEW

• The main 3 causes of plate motion
• MANTLE CONVECTION
• RIDGE PUSH
• SLAB PULL

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The CHANGING CONTINENTS

• Plate tectonics changes the size and shape of
  continents over _____ years
• MILLIONS of
• CRATONS are
• Large areas of stable
  rock.
• Ancient cores that are older than 540 million
  years!

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CRATONS

• CRATONIZATION, formation of cratons, was 2.5
  BILLION years ago.
• Earth's heat flow was nearly three times higher
  than it is today because of the greater
  concentration of radioactive isotopes and the
  residual heat from the Earth's accretion.
• There was considerably greater tectonic and
  volcanic activity the mantle was much more fluid
  and the crust much thinner. This resulted in
  rapid formation of oceanic crust at ridges and
  hot spots, and rapid recycling of oceanic crust
  at subduction zones. Earth's surface was probably
  broken up into many small plates with volcanic
  islands and arcs in great abundance. Small
  protocontinents (cratons) formed as crustal rock
  was melted and remelted by hot spots and recycled
  in subduction zones.
• There were no large continents 2.5 billion years
  ago small protocontinents were probably the
  norm.

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The CHANGING CONTINENTS

• SHIELDS are
• Rocks within cratons that are exposed at the
  surface

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SHIELDS

• A shield is that part of the continental crust in
  which these usually Precambrian basement rocks
  crop out extensively at the surface.
• They have been little affected by tectonic events
  following the end of the Precambrian Era, and are
  relatively flat regions where mountain building,
  faulting, and other tectonic processes are
  greatly diminished compared with the activity
  that occurs at the margins of the shields and the
  boundaries between tectonic plates.

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The CHANGING CONTINENTS RESHAPING EARTHS CRUST

• Crust is reshaped when it gets bigger or smaller.
  
• The continents get smaller through
• RIFTING CONTINENTAL REDUCTION
• The continents grow larger through
• TERRANES CONTINENTAL GROWTH

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RIFTING CONTINENTAL REDUCTION

• a RIFT (noun) is
• a crack or break in the crust
• the process of RIFTING (a verb) is
• the way a rift forms and leads to
• the break up of a continent

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RIFTING CONTINENTAL REDUCTION

• Do scientist KNOW what causes rifting?
• 
  NO
• We think rifting is caused by
• heat from the mantle building up below a
  continent until the lithosphere thins breaks

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TERRANES CONTINENTAL GROWTH

• a TERRANE is
• a piece of lithosphere that has a unique geologic
  history that differs from the histories of the
  surrounding lithosphere
• in other words ODD ROCK that doesnt belong
• Why doesnt it belong?
• It came from somewhere else was mashed on!

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• How can you remember that a terrane is land that
  came from somewhere else and was scraped onto a
  continent by movement of the plates?

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TERRANES CONTINENTAL GROWTH

• The word for what is happening when a continent
  gets bigger by adding on terranes is
• ACCRETION
• How does ACCRETION happen?
• When a tectonic plate with a terrane riding on it
  converges with a continent, the plate UNDER the
  terrane subducts.
• The terrane is scraped off of the subducting
  plate and sticks to the continent making it
  bigger.
• Imagine what would happen if you were on top of a
  train that went under a low bridge ?

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TERRANES CONTINENTAL GROWTH

• How do geologists know that a terrane is NOT part
  of the original craton?
• 1) The terrane contains different rocks fossils
• 2) There are faults at the terrane boundary
• 3) Terrane has different magnetic properties
• Above different means different than what?
• Different than the neighboring rock

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EFFECTS OF CONTINENTAL CHANGE

• When continents move what changes?
• Flow of air moisture changes the climate
• Changing climate ? changes in life in the area

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CHANGES IN CLIMATE

• An example of a climate that changed when
  continents drifted is
• The Sahara desert in Africa was once covered by a
  thick ice sheet when it was attached to the
  supercontinent and near the South Pole.

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CHANGES IN LIFE

• When continents drift what can happen to animal
  populations?
• animal populations may separate
• If animals can not interbreed, each population
  experiences survival of the fittest leading to
  the evolution of new species
• (called geographic isolation in biology)

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The SUPERCONTINENT CYCLE

• During the SUPERCONTINENT CYCLE
• not only did Pangaea, break into smaller
  continents, but scientists also believe that
  someday the continents will join together again
  to form a new supercontinent.

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WHY SUPERCONINENTS FORM

• Supercontinents form as a result of
• plates carrying continental crust moving toward
  convergent boundaries. When they meet, the
  continental crust (will or will not) subduct.
• WILL NOT
• So, the two smaller continents stick together as
  one bigger continent.

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FORMATION of PANGAEA

• About how long ago did Pangaea FORM?
• about 300 million years ago
• The American mountains that formed when Pangaea
  came together are the
• APPALACHIAN MOUNTAINS
• PANTHALASSA is
• the single large ocean that surrounded Pangaea

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BREAKUP of PANGAEA

• Pangaea first broke into 2 continents
• 1)LAURASIA located in the _______ hemisphere
• NORTHERN
• 2)GONDWANALAND mostly in the _hemisphere
• 
  SOUTHERN

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FEATURES of the MODERN CONTINENTS

• The American mountains that formed as continents
  drifted to where they are now
• the ROCKY MOUNTAINS
• In South America
• the ANDES
• In Europe
• the ALPS

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GEOGRAPHY of the FUTURE

• As continents continue to drift Los Angeles will
  move
• NORTH PAST SAN FRANCISCO!