4.5 The Theory of Plate

Tectonics

4.5 The Theory of Plate

Tectonics

ObjectivesObjectives

• Explain the theory of plate tectonics

• Describe the three types of plate boundaries.

• Explain the theory of plate tectonics

• Describe the three types of plate boundaries.

Engage/Explore Engage/Explore

• What is a plate?• Think of other contexts in which the

word is used.

• Metal plates that cover machinery• Home plate in baseball, • a reptile’s plates or scales• plate of photographs in a textbook

• What is a plate?• Think of other contexts in which the

word is used.

• Metal plates that cover machinery• Home plate in baseball, • a reptile’s plates or scales• plate of photographs in a textbook

IntroductionIntroduction

• J. Tuzo Wilson - Canadian scientist.

• He discovered that there are cracks in the continents similar to those on the ocean floor.

• J. Tuzo Wilson - Canadian scientist.

• He discovered that there are cracks in the continents similar to those on the ocean floor.

• Wilson proposed that the lithosphere is broken into separate sections called plates.

• Plates can carry both continents or parts of the ocean floor.

• Wilson proposed that the lithosphere is broken into separate sections called plates.

• Plates can carry both continents or parts of the ocean floor.

Great Rift Valley in East Africa

Great Rift Valley in East Africa

A Theory of Plate MotionA Theory of Plate Motion

• Wilson combined the thoughts of sea-floor spreading, Earth’s plates, and continental drift into a theory.

• A scientific theory is a well-tested concept that explains a wide range of observations.

• Wilson combined the thoughts of sea-floor spreading, Earth’s plates, and continental drift into a theory.

• A scientific theory is a well-tested concept that explains a wide range of observations.

• Plate tectonics is the geological theory that state that pieces of Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle. It explains the formation, movement, and subduction of Earth’s plates.

• Plate tectonics is the geological theory that state that pieces of Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle. It explains the formation, movement, and subduction of Earth’s plates.

How can Earth’s plates move?

How can Earth’s plates move?

• The plates of the lithosphere float on top of the asthenosphere. Convection currents rise in the asthenosphere and spread out beneath the lithosphere.

• The plates of the lithosphere float on top of the asthenosphere. Convection currents rise in the asthenosphere and spread out beneath the lithosphere.

Earth’s Lithospheric PlatesEarth’s Lithospheric Plates

Affects of the platesAffects of the plates

• Collide• Pull apart• Grind past each

other

• Collide• Pull apart• Grind past each

other

• Volcanoes• Mountain ranges• Deep-sea

trenches

• Volcanoes• Mountain ranges• Deep-sea

trenches

Earth’s Lithospheric PlatesEarth’s Lithospheric Plates

• P. 133 Figure 23• Which plates include only ocean

floor?• Which plates include both

continents and ocean floor?

• P. 133 Figure 23• Which plates include only ocean

floor?• Which plates include both

continents and ocean floor?

Plate Boundaries Plate Boundaries • Demonstration• Materials - 2 woooden blocks• Three types of blocks

1. Transform boundary - slide past 2. Divergent boundary - pull away

3. Convergent boundary - push two blocks together.

• Draw the blocks with labels and arrows showing the direction of each block’s movement.

• Demonstration• Materials - 2 woooden blocks• Three types of blocks

1. Transform boundary - slide past 2. Divergent boundary - pull away

3. Convergent boundary - push two blocks together.

• Draw the blocks with labels and arrows showing the direction of each block’s movement.

Flat rock demonstrationFlat rock demonstration

• Demonstrate the boundaries using rocks. • Why do you think earthquakes occur

frequently at transform boundaries?• Answer: The plates cannot move

smoothly past one another because of the irregular nature of faults.

• How fast do you think Earth’s plates are moving?

• Answer: Only a few centimenters per year.

• Demonstrate the boundaries using rocks. • Why do you think earthquakes occur

frequently at transform boundaries?• Answer: The plates cannot move

smoothly past one another because of the irregular nature of faults.

• How fast do you think Earth’s plates are moving?

• Answer: Only a few centimenters per year.

Plate BoundariesPlate Boundaries

• Faults - breaks the Earth’s crust where rocks have slipped past each other which form along these boundaries.

• Three kinds of boundaries

• Faults - breaks the Earth’s crust where rocks have slipped past each other which form along these boundaries.

• Three kinds of boundaries

Transform BoundaryTransform Boundary

• A place where two plates slip past each other, moving in opposite directions.

• Earthquakes occur along these boundaries.

• San Andreas Fault is an example. The Pacific plate is sliding past the North American plate.

• Crust is neither created nor destroyed.

• A place where two plates slip past each other, moving in opposite directions.

• Earthquakes occur along these boundaries.

• San Andreas Fault is an example. The Pacific plate is sliding past the North American plate.

• Crust is neither created nor destroyed.

San Andreas FaultSan Andreas Fault

San Andreas FaultSan Andreas Fault

Divergent BoundaryDivergent Boundary

• The place where two plates move apart.

• Most occur at the mid-ocean ridge and on land.

• The boundary forms rift valleys.

• Example - Great Rift Valley has a 3000 km crack.

• The place where two plates move apart.

• Most occur at the mid-ocean ridge and on land.

• The boundary forms rift valleys.

• Example - Great Rift Valley has a 3000 km crack.

Rio Grande RiftRio Grande Rift

• Extendsfrom central Colorado to El Paso, Texas.

• Extendsfrom central Colorado to El Paso, Texas.

Exploring Exercise - Plate Tectonics

Exploring Exercise - Plate Tectonics

Plate Tectonics - p. 134-135What is magma?What is the magma coming from

that is shown erupting through the mid-ocean ridge and the rift valley?

Answer: asthenosphereWhat new process are shown?

Plate Tectonics - p. 134-135What is magma?What is the magma coming from

that is shown erupting through the mid-ocean ridge and the rift valley?

Answer: asthenosphereWhat new process are shown?

Convergent BoundariesConvergent Boundaries

• Two plates come together. This is called a collision

• When two continental plates collide, why isn’t one subducted beneath the other?

Appalachian Mountains formed when two continental plates collided.

-The density of plates determines which plate comes out on top.

• Two plates come together. This is called a collision

• When two continental plates collide, why isn’t one subducted beneath the other?

Appalachian Mountains formed when two continental plates collided.

-The density of plates determines which plate comes out on top.

Appalachian MountainsAppalachian Mountains

Appalachian MountainsAppalachian Mountains

Convergent BoundariesConvergent Boundaries

Oceanic/oceanic Subduction occurs

Oceanic/continental Oceanic plate sinks

Continental/continental Mountain ranges form

Candy Bar Inquiry Challenge

Candy Bar Inquiry Challenge

• Material - candy bar, paper towel• Procedure

– Wash hands– Give out Snickers– How can you use this candy bar to

model what happens at divergent and convergent boundaries?

– Make a sketch of what you see.

• Material - candy bar, paper towel• Procedure

– Wash hands– Give out Snickers– How can you use this candy bar to

model what happens at divergent and convergent boundaries?

– Make a sketch of what you see.

The Continents’ Slow Dance

The Continents’ Slow Dance

• The continents move at slow rates: one to ten centimeters per year.

• Pages 136-137 Read Figure 26• Pangea began to drift apart about

225 million years ago.

• The continents move at slow rates: one to ten centimeters per year.

• Pages 136-137 Read Figure 26• Pangea began to drift apart about

225 million years ago.