Plate Tectonics EQ: What is the theory of plate tectonics?

Plate Tectonics

EQ: What is the theory of plate tectonics?

Plates

• A section of the lithosphere that slowly moves, carrying pieces of continental and oceanic crust

• The plates fit closely together along cracks in the crust

• Plates carry the continents or parts of the ocean floor, or both


Scientific Theory

• A well – tested concept that explains a wide range of observations


Plate Tectonics

• A geological theory that states that pieces of Earth’s crust are in constant, slow motion, driven by convection currents in the mantle

• Convection Currents: The movement of a fluid, caused by differences in temperature and density, that transfers heat from one part of the fluid to another


How can Earth’s plates move?

• The plates of the lithosphere float on the top of the asthenosphere

• Convection currents rise in the asthenosphere and spread out beneath the lithosphere

• Geologists believe this causes plate movement


As plates move, they collide, pull apart, or grind past each other, producing spectacular changes in the earth’s surface.


These changes include volcanoes, mountain ranges, deep sea trenches, and earthquakes.


Figure 26: Interpreting MapsWhich plates include only ocean floor? Which plates include both continents and ocean floor?

• Plates that include only ocean floor are the Pacific Plate and the Nazca Plate

• All other labeled plates in the figure include both continents and ocean floor


Study the map of Earth’s plates in Figure 26. Notice the arrows that show the direction of plate movement. Now find the Nazca plate on the map. What direction is it moving?

• The Nazca plate is moving east

EQ: What is the theory of

plate tectonics?

Find the South American plate and describe its movement.

• The South American plate is moving west

EQ: What is the theory of plate

tectonics?

What do you think will happen as these plates continue to move?

• If the plates continue to move, they will collide (convergent boundary)

• Since the Nazca plate carries oceanic crust and the South American plate carries continental crust, the Nazca will plunge beneath the South American plate


tectonics?

Faults

• A break in the Earth’s crust where slabs of rock slip past each other


three types of plate boundaries• Transform Boundaries

• Divergent Boundaries

• Convergent Boundaries

• At each type of plate boundary, there is a different type of plate movement

EQ: What is the

theory of plate

tectonics?

Transform Boundaries

• A plate boundary where two plates move past each other in opposite directions

• Crust is neither created nor destroyedEQ: What is the theory

of plate tectonics?

What Earth changing event occurs on a transforming boundary?

• Earthquakes frequently occur at transform boundaries


Divergent boundaries

• A plate boundary where two plates move away from each other

• Most divergent boundaries occur at the mid-ocean ridge

• Divergent boundaries that occur on land are called rift valleys

• Example: Great Rift Valley (South Africa)

– A 3,000 km crack in the earth


Rift Valleys

• A rift valley is a deep valley that forms along a divergent boundary on land

• Rift valleys form as two slabs of Earth’s crust slide apart


tectonics?

What could eventually happen at the Great Rift Valley in Africa?

• The rift may someday split the eastern part of Africa away from the rest of the continent


Convergent Boundaries

• A plate boundary where two plates move toward each other

• Collisions can occur between:– oceanic crust and oceanic crust – oceanic crust and continental crust– continental crust and continental

crustEQ: What is the theory of plate tectonics?

When two plates collide, the density of the plates determines which one comes out on top.


plate tectonics?

What occurs when plates carrying oceanic crust collide?

• The more dense plate dives back into the mantle (subduction)

• The collision between oceanic plates causes deep-ocean trenches


tectonics?

What occurs when plates carrying oceanic and continental crust collide?

• The more dense oceanic crust sinks and plunges (subducts) beneath the less dense continental crust

• The collision between oceanic plates and continental plates can cause a volcanic eruption


What occurs when plates carrying continental crust collide?

• Plates crash head – on causing mighty mountain ranges


tectonics?

What types of plate movement occur at plate boundaries?

• Plates slip past each other at transform boundaries

• Move apart at divergent boundaries

• Come together at convergent boundaries


plate tectonics?

Plates move at a rate of between one and ten centimeters per year.


The North American and Eurasian plates float away from each other at a rate of fingernail growth. This is a rate of 2.5 centimeters per year.


plate tectonics?

Figure 29: Posing QuestionsWhat questions would you need to answer in order to predict where the continents will be in 50 million years?

• You would need answers to how fast and in what direction each plate is moving


Plate Tectonics EQ: What is the theory of plate tectonics?

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