1. How are the agents of weathering similar and different? 2. How does erosion affect Earth's surface?

3. Give an example of each: how water can wear down Earth's surface over a short period of time and a very long period of time.

4. What is mechanical weathering? Give an example.

5. What is chemical weathering? Give an example.

1- They all break down and dissolve rocks, though some use physical force and some use chemical processes.

2- Erosion breaks rocks down further and then moves them. Forces like wind and water move the rock pieces. They mix with matter like sand to become sediment. Weathering and erosion help shape Earth's surface.

3- Flowing water can move rocks, causing them to rub together and wear down into rounded shapes. When plants grow in cracks in a rock, their roots can widen the cracks and force the rock apart. Rainwater fills small cracks in a rock. As the water freezes, it expands, widening the cracks and splitting apart the rock.

A rock will weather until it is a tiny grain of sand. Water moving across the earth in streams and rivers pushes along soil and breaks down pieces of rock in a process called erosion. The moving water carries away rock and soil from some areas and deposits them in other areas, creating new landforms or changing the course of a stream or river.

4- Mechanical weathering involves mechanical processes that break up a rock: for example, ice freezing and expanding in cracks in the rock; tree roots growing in similar cracks; expansion and contraction of rock in areas with high daytime and low nighttime temperatures; cracking of rocks in forest fires, and so forth.

5- The reaction of carbon dioxide gas in rainwater can produce carbonic acid that dissolves some minerals, especially limestone. Acid rain caused by pollution such as factory and car exhaust is another agent of chemical weathering. Chemical weathering also occurs when iron in rock oxidizes or rusts.