Earth’s Changing Surface

Earth’s Changing Surface

Middle School

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Learning Objectives

• Tell the difference between processes that build up and wear down the Earth's surface.

• Explain plate tectonics and describe the three main types of plate boundaries.

• Define and tell the difference between weathering, erosion, and deposition.

• Compare slow and sudden changes to the Earth's surface, giving examples of each.

Key Vocabulary

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Plate Tectonics

The theory that Earth's lithosphere is broken into large, rigid pieces that move slowly.

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Asthenosphere

A hot, flowing layer in the mantle that the Earth's tectonic plates move on.

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Weathering

The destructive process that breaks down rocks and soil into smaller pieces through various forces.

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Erosion

The destructive process of transporting weathered rock and soil by natural forces like wind and water.

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Deposition

The constructive process where transported sediment is dropped, building up new landforms like deltas or dunes.

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How the Earth's Surface Changes

Constructive Processes

• ​Constructive processes are responsible for building up land and creating new landforms on the Earth's surface.

• ​​These changes are often gradual, taking place over thousands or even millions of years to complete.

• ​An example of a constructive process is a volcano erupting and forming a new island.

Destructive Processes

• ​Destructive processes are responsible for wearing down or breaking apart the Earth's existing surface features.

• ​​These changes can be catastrophic, happening very quickly, sometimes in just a few moments.

• ​Earthquakes are a destructive process caused by the movement of plates in the lithosphere.

Multiple Choice

Forces that build up surface features or create new landforms are called:

• Tectonic forces

• Destructive forces

• Constructive forces

• Erosional forces

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What Is the Theory of Plate Tectonics?

• Earth’s lithosphere is broken into 15 tectonic plates that move on the asthenosphere.

• Movement is driven by convection currents and helped by the process of subduction.

• All continents were once joined in a supercontinent named Pangea.

• Scientists use the Global Positioning System (GPS) to measure this plate movement today.

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Multiple Choice

What is the primary mechanism that causes the movement of tectonic plates?

• The Earth's magnetic field

• The gravitational pull of the moon

• Convection currents in the asthenosphere

• Wind and water erosion on the surface

Types of Plate Boundaries

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Divergent Boundary

• Two tectonic plates are moving away from each other.

• Magma from the asthenosphere can rise to the surface.

• This creates new crust and may form undersea volcanoes.

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Convergent Boundary

• This is where two plates move toward each other.

• The collision causes one plate to go under the other.

• This can form mountains, volcanic arcs, and powerful earthquakes.

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Transform Boundary

• Two plates slide past each other in a horizontal motion.

• The friction between the plates can cause them to lock.

• This built-up stress is eventually released as an earthquake.

Multiple Choice

A boundary where two plates slide past each other horizontally, often causing earthquakes, is known as a:

• Convergent Boundary

• Transform Boundary

• Divergent Boundary

• Subduction Zone

Reshaping the Land

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Weathering

• Weathering breaks down rocks and soil into smaller pieces called sediment.

• It is a destructive process that changes the Earth's surface.

• This is caused by wind, water, ice, and temperature changes.

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Erosion

• Erosion is a destructive process that moves sediment to new places.

• Natural forces like flowing water, wind, and glaciers cause erosion.

• The speed of erosion is affected by land slope and water speed.

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Deposition

• Deposition is a constructive process that drops sediment in new locations.

• It happens when forces like wind or water slow down.

• This process builds new landforms like deltas, beaches, and sand dunes.

Multiple Choice

A river carrying sediment flows into the ocean and drops the sediment at the mouth, forming a delta. This is an example of which process?

• Subduction

• Deposition

• Erosion

• Weathering

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Clearing Up Common Misconceptions

Misconception	Correction
Earth's surface has always looked the same and does not move.	The surface is always changing due to plate tectonics, forming continents like Pangea.
Tectonic plates move very quickly.	Plate movement is very slow, only a few centimeters per year.
Weathering and erosion are the same process.	Weathering breaks down rocks, while erosion moves the broken pieces away.

Multiple Choice

How do constructive and destructive processes differ in their effect on the Earth's surface?

• Constructive processes build land, while destructive processes wear it down.

• Constructive processes happen quickly, while destructive processes happen slowly.

• Constructive processes are caused by water, while destructive processes are caused by wind.

• Constructive processes form mountains, while destructive processes form volcanoes.

Multiple Choice

Which statement best explains the relationship between the lithosphere and the asthenosphere?

• The rigid plates of the lithosphere move on the flowing asthenosphere.

• The asthenosphere is the source of water for erosion on the lithosphere.

• The lithosphere and asthenosphere are two names for the same layer of the Earth.

• The flowing asthenosphere is broken into plates that move on the rigid lithosphere.

Multiple Choice

A coastal area has its vegetation removed for a new housing development.

Based on your understanding of Earth's processes, what is the most likely consequence?

• The rate of weathering will decrease because there is less organic activity.

• The rate of erosion will increase because fewer plant roots are left to hold the soil in place.

• The rate of deposition will increase because the houses will block the wind.

• A transform plate boundary will form due to the change in surface weight.

Multiple Choice

Geologists discover a long chain of mountains on the seafloor where two plates are moving apart. Analyze this situation to determine the primary process occurring.

• This is a convergent boundary where two oceanic plates are colliding to push up mountains.

• This is a divergent boundary where magma is rising to form new crust and undersea mountains.

• This is a transform boundary where friction is causing the seafloor to buckle into mountains.

• This is a zone of rapid deposition that has built up a mountain range under the sea.

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Summary

• Earth’s surface is always changing due to gradual and catastrophic events.

• Constructive forces build up land, while destructive forces wear it down.

• Plate tectonics explains how moving plates cause earthquakes, volcanoes, and mountains.

• Weathering, erosion, and deposition work together to reshape Earth's surface features.

Poll

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

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