Tectonic Plates

Tectonic Plates

Middle School

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Learning Objectives

• Define plate tectonics and describe the evidence for continental drift.

• Describe the layers of the Earth and the process of plate movement.

• Compare and contrast the three types of plate boundaries.

• Explain how plate movements cause earthquakes, volcanoes, and mountain formation.

Key Vocabulary

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Plate Tectonics

The theory that Earth's surface is broken into large, rigid, and always moving pieces.

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Continental Drift

The idea that continents have slowly moved to where they are on Earth's surface today.

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Subduction

The process where a denser tectonic plate is forced to slide down beneath another plate.

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Seafloor Spreading

The process that creates new oceanic crust at boundaries where tectonic plates are moving apart.

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Mantle Convection

The circular flow of rock in the mantle that acts as the main driving force for plate movement.

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What Are Tectonic Plates?

• Earth’s outer layer, the lithosphere, is broken into large pieces.

• These pieces are called tectonic plates, and they are always moving slowly.

• The theory of plate tectonics explains how and why they move.

• Their movements cause earthquakes and form volcanoes and mountains.

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Multiple Choice

According to the theory of plate tectonics, what is the primary reason for the occurrence of earthquakes and the formation of mountain ranges?

• The gravitational pull of the moon.

• The rotation of the Earth on its axis.

• The movement and interaction of tectonic plates.

• The process of erosion and weathering.

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What Is Continental Drift?

• Continents were once a single supercontinent, Pangaea, that later split apart.

• The coastlines of Africa and South America appear to fit together like puzzles.

• Matching ancient fossils are found on continents now separated by wide oceans.

• Alfred Wegener used these observations to support his continental drift hypothesis.

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Multiple Choice

What key pieces of evidence did Alfred Wegener use to support his hypothesis of continental drift?

• The puzzle-like fit of continents and cross-continental fossil evidence.

• The presence of volcanoes and the occurrence of earthquakes.

• The depth of the oceans and the height of mountains.

• The differing climates on various continents.

Earth's Structure & Plate Movement

• Earth's rigid lithosphere moves on the slowly flowing asthenosphere below it.

• Plates can be made of continental crust or denser oceanic crust.

• The main driving force for plate movement is mantle convection.

Multiple Choice

What is the primary driving force behind the movement of Earth's tectonic plates?

• The Earth's magnetic field.

• Wind and ocean currents on the surface.

• Convection currents in the mantle.

• The gravitational pull of the sun.

Types of Plate Boundaries

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Divergent Boundary

• ​Two tectonic plates move away from each other.

• ​​Magma rises from the mantle to fill the gap.

• ​This process creates new crust, forming mid-ocean ridges.

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Convergent Boundary

• ​Two tectonic plates move toward each other and collide.

• ​​An oceanic plate can slide under another, causing volcanoes.

• When two continental plates collide, their edges crumple and rise due to their low density, forming large mountain ranges.

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Transform Boundary

• ​Two tectonic plates slide horizontally past one another.

• ​​Friction can cause the plates to get stuck together.

• The sudden release of pressure results in powerful earthquakes.

Multiple Choice

Which type of plate boundary is characterized by two plates sliding horizontally past each other, often causing earthquakes?

• Divergent Boundary

• Transform Boundary

• Subduction Zone

• Convergent Boundary

Related Geological Phenomena

• The Pacific 'Ring of Fire' has many earthquakes and volcanic eruptions.

• This happens along the plate boundaries circling the Pacific basin.

• The Cascadia Subduction Zone can cause massive earthquakes in North America.

Multiple Choice

What is the 'Ring of Fire'?

• The area around the Earth's core.

• A transform boundary in California.

• A large desert that circles the Earth's equator.

• A chain of active volcanoes and earthquake sites along plate boundaries in the Pacific Ocean.

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Common Misconceptions About Plate Tectonics

Misconception	Correction
Continents float on the oceans like boats.	Tectonic plates move over the flowing asthenosphere in the upper mantle.
Tectonic plates move very quickly.	Plates move slowly, about the same speed that fingernails grow.
All plate collisions create huge mountains.	Some collisions create mountains, while others result in subduction.
Earthquakes only happen when plates slide past each other.	Earthquakes occur at colliding, separating, and sliding boundaries.

Multiple Choice

If you were studying a mid-ocean ridge, what process would you be observing and what type of plate boundary would be present?

• Seafloor spreading at a divergent boundary.

• Subduction at a convergent boundary.

• Friction buildup at a transform boundary.

• Mountain formation at a convergent boundary.

Multiple Choice

Why do large mountain ranges like the Himalayas form when two continental plates collide?

• Because both plates have low density, preventing subduction and causing the crust to crumple upwards.

• Because the plates are moving away from each other, allowing mountains to rise in between.

• Because one plate melts and pushes the other plate up.

• Because of intense volcanic activity that deposits lava in layers.

Multiple Choice

Based on the concept of mantle convection, what would likely happen to plate movement if the Earth's mantle cooled down significantly?

• Plate movement would not be affected as it is driven by surface forces.

• Plate movement would speed up because the cooler mantle would be denser.

• Plate movement would become more erratic and unpredictable.

• Plate movement would slow down or stop because the driving convective currents would weaken or cease.

Multiple Choice

The San Andreas Fault is a transform boundary known for frequent earthquakes. What happens at this boundary to cause these earthquakes?

• The plates sliding past each other build up friction and pressure, which is released as an earthquake.

• The plates separating allows magma to rise, which triggers earthquakes.

• The plates colliding cause the ground to crumple and fold, resulting in earthquakes.

• The subduction of one plate under another melts rock and causes seismic waves.

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Summary

• Earth's surface is divided into tectonic plates that move due to mantle convection.

• Continental drift is supported by fossil evidence and explains the movement of continents.

• New crust is formed at divergent boundaries and recycled at convergent boundaries.

• Transform boundaries are common locations for earthquakes, and the Ring of Fire is a result of plate activity.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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