Moistened soil, paper, wood, sand appear darker than dry. Why?

Dry material has a rough surface. Therefore, the reflected light is scattered. If the material is moistened, the roughness will decrease. In addition, in a thin film of water, light undergoes multiple total reflection and absorption.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.