Question

Which of the following is an agent of chemical weathering? A. ice wedging B. burrowing animals C. carbonic acid D. growing tree roots

Short answer

C. Carbonic acid is an agent of chemical weathering.

Step-by-step solution

Understand Chemical Weathering

Chemical weathering refers to the decomposition or alteration of minerals and rocks caused by chemical reactions, typically with water and other chemicals often found in the environment. This contrasts with physical weathering, such as ice wedging, where material breakdown is due to physical forces.

Analyze Each Option

A. Ice wedging is a type of physical weathering where water enters cracks, freezes, and then expands, breaking the rock apart. B. Burrowing animals physically break down rocks into smaller pieces, another example of physical weathering. C. Carbonic acid, formed when carbon dioxide reacts with water, can dissolve rocks and minerals—particularly limestone—through a chemical process. D. Growing tree roots exert physical pressure on rocks as they grow, which is another form of physical weathering.

Identify the Agent of Chemical Weathering

From the options given: - A (Ice wedging), B (Burrowing animals), and D (Growing tree roots) are all examples of physical weathering. - C (Carbonic acid) is involved in chemical reactions with rocks, specifically those that involve mineral dissolution or alteration, such as the transformation of feldspar into clay.

Key concepts

Carbonic Acid and Chemical Weathering

Carbonic acid plays a crucial role in the process of chemical weathering. This acid is formed when carbon dioxide (\(CO_2\)) from the atmosphere dissolves in water (\(H_2O\)), creating a weak acid known as carbonic acid (\(H_2CO_3\)). This natural acidity is responsible for some of the geological changes we see in the Earth's crust.

• When carbonic acid comes into contact with certain minerals, such as those found in limestone or marble, it can lead to their dissolution.
• This reaction not only changes the structure of the minerals but also tends to weaken rocks over time.
• One common output of this chemical reaction is bicarbonate (\(HCO_3^-\)), which gets washed away by rainwater, further contributing to the weathering process.

This continuous cycle of carbonic acid reacting with minerals is a fundamental aspect of the Earth's natural environment and plays an important role in shaping landscapes.

Mineral Decomposition in Chemical Weathering

Mineral decomposition is a key aspect of chemical weathering, involving the breakdown of minerals into new substances. This transformation occurs when minerals react with water, oxygen, or other natural acids, leading to changes in their chemical structure and composition.
One of the most studied examples of this decomposition is the transformation of the mineral feldspar into clay minerals such as kaolinite.

• Feldspar is a common mineral in the Earth's crust, and its decomposition is a primary contributor to soil formation.
• The reaction with carbonic acid is essential, where water and \(CO_2\) create an acidic environment that facilitates the decomposition.
• This process not only alters the mineral itself but also generates new materials, enriching the soil with nutrients beneficial for plant life.

The continuous breakdown and alteration of minerals through chemical reactions are crucial for recycling elements within the Earth's biosphere.

Rock Alteration Through Chemical Weathering

Rock alteration is a fundamental outcome of chemical weathering, where rocks undergo significant changes in their physical and chemical properties. This alteration typically results from long-term exposure to chemical agents such as carbonic acid, which can penetrate deep into rock structures.

• Over time, the internal structure of rocks becomes less dense, making them more susceptible to further weathering and erosion.
• This process is predominant in sedimentary rocks like limestone, where carbonic acid causes notable wear.
• Such rocks can develop features like caves and sinkholes as a result of prolonged chemical weathering.

Understanding rock alteration processes helps geologists predict changes in landscapes and evaluate risks in geological stability.