Weathering and erosion

What this chapter teaches

Weathering breaks rock where it lies. Water that freezes in a crack gets about 9 percent bigger and pushes the crack wider. Heat and cold, and growing roots, also break rock. Erosion carries the pieces away by river, wind and waves, and the pieces get smaller and rounder as they go.

Three questions to ask

There is no one right wording. Listen for the idea.

1. What is the difference between weathering and erosion?
2. Why does a crack in a rock get wider when water freezes in it?
3. Why are stones at the mouth of a river smaller and rounder than stones near the top?

After the chapter, the learner can

• Explain how heat, water, ice and roots break up rocks
• Explain how rivers, wind and waves carry rock away