Final answer:
The crumbling of a sidewalk due to weeds growing in the cracks is an example of mechanical weathering, which physically breaks down Earth materials. This process is part of the larger weathering phenomena that create soil by breaking down rocks through physical and chemical means without altering the rocks' chemical composition.
Step-by-step explanation:
Mechanical Weathering
When weeds grow through cracks in the sidewalk and cause it to crumble, this is an example of mechanical weathering. This natural process occurs when physical forces break down rocks and other Earth materials without altering their chemical composition. One common agent of mechanical weathering is the expansion of plant roots within the cracks of rocks or pavement. As the plants grow, their roots expand and exert pressure on the surrounding material, eventually causing it to break apart.
Processes of Weathering and Soil Formation
This phenomenon is closely related to the overall processes of weathering, which contribute to the creation of soil. Chemical weathering takes place when chemical reactions decompose or alter the composition of rocks, while mechanical weathering physically breaks down rocks and minerals. Over time, weathering contributes to the development of soil layers or soil horizons as different size particles settle and accumulate.
Both mechanical and chemical weathering play crucial roles in the Earth's geological cycle, and both can be agents of change that affect the environment and man-made structures like sidewalks.