Explanation:

- Option 1: Weathering

- This is the breaking down and decay of rocks in their natural place by physical, chemical, and biological processes.

- Temperature changes, frost action, plants, animals, and human activities all contribute.

- Option 2: Smelting

- This is a metallurgical process to extract metals from their ores by heating and melting.

- Option 3: Deforestation

- This refers to the large-scale removal of forests, impacting ecosystems and climate but unrelated to rock decay.

- Option 4: Erosion

- This involves the movement of rock particles by wind, water, or ice, not breaking them in place.

- Answer: Option 1 - Weathering