Weathering

Weathering

Middle School

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Learning Objectives

• Define weathering and explain how it is different from erosion.

• Describe the three main types of weathering: physical, chemical, and biological.

• Explain the different causes of physical and chemical weathering.

• Identify the key factors that affect how quickly rocks weather.

Key Vocabulary

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Weathering

The breaking down or dissolving of rocks and minerals on the surface of the Earth.

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Physical Weathering

This is the process that breaks rocks apart without changing their basic chemical composition.

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Chemical Weathering

This is the breakdown of rocks caused by chemical reactions that change their overall composition.

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Abrasion

This is when rocks are smoothed by other particles carried by sand, water, or wind.

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Oxidation

This is the reaction of iron in rocks with oxygen, which is what produces rust.

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Hydrolysis

This is a chemical breakdown of a substance within a rock when it combines with water.

What Is Weathering?

• Weathering is the natural process that breaks down rocks and minerals.

• It can happen through physical or chemical processes.

• Weathering breaks rocks, while erosion moves the pieces to a new location.

Multiple Choice

What is the main difference between weathering and erosion?

• Weathering and erosion are the exact same process.

• Weathering breaks down rocks, while erosion moves the broken pieces.

• Weathering only happens with water, and erosion only happens with wind.

• Weathering moves rocks, while erosion breaks them down.

Physical (Mechanical) Weathering

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Ice Wedging

• ​Water seeps into small cracks or pores in rocks.

• ​​When the water freezes into ice, it expands forcefully.

• ​This repeated freezing and thawing wedges the rock apart.

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Abrasion

• ​Rocks are worn down by friction from other particles.

• ​​Wind, water, and glaciers carry these scraping particles.

• ​This makes rocks become smoother and more rounded.

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Plants and Animals

• ​Plant roots can grow into cracks, forcing them wider.

• ​​This process is also known as root wedging action.

• ​Burrowing animals also dig and break weaker rocks apart.

Multiple Choice

Which of the following is an example of physical weathering?

• An iron nail turning to rust.

• Limestone being worn away by acid rain.

• A tree root growing into a crack in a rock and splitting it.

• A rock dissolving in acid.

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What Is Chemical Weathering?

• Chemical weathering breaks down rocks with reactions, creating totally new substances.

• Water can dissolve minerals in rocks, and oxidation occurs when oxygen reacts with iron to form rust.

• Carbon dioxide (CO₂) in rain forms a weak acid that weathers rock.

• Organisms like lichens produce weak acids that dissolve the surface of rocks.

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Multiple Choice

When iron in a rock reacts with oxygen and water to form rust, what type of weathering is occurring?

• Oxidation

• Hydrolysis

• Carbonation

• Abrasion

Biological Weathering & Rate of Weathering

• Plants and animals cause weathering by breaking or dissolving rocks.

• Weathering happens fastest in warm, wet climates.

• Softer rocks with more holes weather much more quickly.

Multiple Choice

In which environment would a rock weather the fastest?

• A cold, dry desert

• A frozen polar region

• A warm, humid rainforest

• A temperate, dry grassland

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Common Misconceptions about Weathering

Misconception	Correction
Weathering and erosion are the same.	Weathering breaks rocks down; erosion moves the pieces away.
Weathering is always a slow process.	Some events, like acid rain, can cause very rapid weathering.
Rocks are permanent and do not change.	All rocks on Earth's surface are constantly being changed by weathering.

Multiple Choice

How does the action of lichens on a rock differ from the action of ice wedging?

• Lichens cause chemical weathering by producing acid, while ice wedging causes physical weathering by expansion.

• Both are forms of chemical weathering, but ice wedging requires water.

• Lichens cause physical weathering, while ice wedging causes chemical weathering.

• Both are forms of physical weathering, but lichens are biological.

Multiple Choice

Why does a permeable rock weather faster than an impermeable rock in the same wet climate?

• The color of permeable rocks absorbs more heat, speeding up reactions.

• Permeable rock is always softer and easier to break.

• Impermeable rocks are always made of minerals that don't react with water.

• Water can get inside the permeable rock, allowing for chemical and physical weathering to occur internally.

Multiple Choice

A limestone statue is in a city with heavy pollution from burning coal. Predict the primary type of weathering it will experience and why.

• Physical weathering from abrasion, because of city wind.

• Chemical weathering from oxidation, because of the iron in the limestone.

• Physical weathering from ice wedging, because city temperatures fluctuate.

• Chemical weathering from acid rain, because pollutants like sulfur oxides react with rainwater.

Multiple Choice

What is the main difference between physical and chemical weathering?

• A physical change creates a new substance, while a chemical change alters the rock's shape.

• A physical change is irreversible, while a chemical change is reversible.

• A physical change alters the form of the rock but not its chemical composition, while a chemical change creates a new substance.

• A physical change only happens to soft rocks, while a chemical change only happens to hard rocks.

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Summary

• Weathering breaks rocks down, and erosion moves the broken pieces away.

• Physical weathering changes a rock's size; chemical weathering creates new substances.

• Living things can cause both physical and chemical weathering on rocks.

• Weathering happens fastest in warm, wet climates on softer rock types.

Poll

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

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