Weathering: Physical, Chemical, Biological
Weathering: Physical, Chemical, Biological
- Unit 1: Earth & Rocks
- Unit 2: Tectonics & Space
- Unit 3: Chemistry & Atmosphere
- Unit 4: Ecosystems & Biology
🎯 In this topic you will
- Describe the process of weathering and how it differs from erosion
- Explain physical weathering and how temperature and freezing affect rocks
- Describe chemical weathering and how reactions like oxidation and carbonation occur
- Understand biological weathering caused by plants, lichens, and animals
- Explore how different types of weathering interact and contribute to the rock cycle
🧠 Key Words
- weathering
- physical weathering
- chemical weathering
- biological weathering
- freeze-thaw
- oxidation
- hydrolysis
- carbonation
- exfoliation
- sediment
Show Definitions
- weathering: The breakdown of rocks into smaller pieces at or near Earth's surface without being moved.
- physical weathering: The mechanical breakdown of rocks without changing their chemical makeup.
- chemical weathering: The breakdown of rocks through chemical changes, often involving water, acids, or oxygen.
- biological weathering: The breakdown of rocks caused by living organisms like plants, lichens, and animals.
- freeze-thaw: A process where water freezes in rock cracks, expands, and causes the rock to split.
- oxidation: A chemical reaction where minerals react with oxygen, often forming rust-like substances.
- hydrolysis: A reaction between water and minerals that changes their structure, like turning feldspar into clay.
- carbonation: A process where acidic rainwater reacts with carbonate minerals, dissolving rocks like limestone.
- exfoliation: The peeling of rock layers due to temperature changes causing expansion and contraction.
- sediment: Small particles of rock or mineral that result from weathering and may form sedimentary rock.
🧱 Types of Weathering
Weathering is the process that breaks down rocks and minerals at or near the Earth’s surface into smaller pieces, without moving them from their original location. Unlike erosion, which involves movement, weathering changes the shape and structure of rocks in place. It is the first step in the breakdown of rocks and the formation of sediments, which may eventually become part of sedimentary rocks through the rock cycle. There are three main types of weathering: physical, chemical, and biological.
🧪 Did you know?
Some weathering processes on Earth also occur on other planets, like Mars, where wind and dust storms have shaped rock formations for millions of years — without any liquid water!
❄️ Physical Weathering
Physical weathering, also called mechanical weathering, happens when rocks are broken down into smaller pieces without changing their chemical composition. This type of weathering is usually caused by physical forces such as temperature changes, frost action, wind, or abrasion. One common example is freeze-thaw weathering, where water enters cracks in rocks, freezes, and expands. As water turns into ice, it takes up more space, forcing the crack to widen. Repeated freezing and thawing eventually causes the rock to split apart. Another example is exfoliation, where layers of rock peel off due to heating and cooling cycles, especially in desert environments. Over time, these processes can reduce even large boulders into gravel or sand.
📌 Important Concept
Freeze-Thaw Weathering: When water enters cracks in rocks and freezes, it expands, widening the cracks. Repeated freezing and thawing eventually causes the rock to break apart.
🧪 Chemical Weathering
Chemical weathering involves the alteration of the rock’s chemical structure, often through reactions with water, oxygen, acids, or other chemicals in the environment. One of the most common forms is oxidation, where minerals in the rock react with oxygen in the air or water, forming oxides such as rust. Another major process is hydrolysis, where water reacts with minerals like feldspar in granite to form clay minerals. In areas with acid rain or high carbon dioxide levels, carbonation can also occur. This happens when rainwater, slightly acidic due to dissolved carbon dioxide, reacts with calcium carbonate in rocks like limestone, causing it to slowly dissolve. Chemical weathering tends to be more effective in warm, wet climates, where water and biological activity are abundant.
⚠️ Common Mistake
Don’t assume chemical weathering only occurs in polluted areas — natural processes like carbonation and oxidation happen even in clean, rural environments.
🌱 Biological Weathering
Biological weathering occurs when living organisms contribute to the breakdown of rock. This can happen in several ways. For instance, plant roots can grow into tiny cracks in rocks as they seek moisture and nutrients. As the roots grow and thicken, they force the cracks to expand, eventually breaking the rock apart. Lichens and mosses that grow on rock surfaces produce weak acids that chemically break down the minerals in the rock. Even burrowing animals can expose deeper layers of rock to air and moisture, speeding up weathering. Biological weathering is often closely connected to both physical and chemical processes, and it plays an important role in shaping soil and surface landscapes.
🔄 Weathering in Combination
These types of weathering often act together. For example, a rock may be weakened by chemical weathering, making it more likely to crack under physical stress. Or plant roots may both physically split a rock and release acids that cause chemical changes. Over time, weathering can reduce even the hardest rocks into fine sediments, which can be moved by erosion, compacted, and eventually become part of a new rock through the rock cycle. In this way, weathering is not just a surface process — it is a key part of how Earth recycles and reshapes its crust.
❓ QUESTIONS
1. What is the difference between weathering and erosion?
👀 Show answer
2. How does freeze-thaw weathering break rocks apart?
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3. Give one example of chemical weathering and explain how it works.
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4. How do plants contribute to biological weathering?
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5. Why do weathering processes often work together?