The term "outer layer" refers to the external covering or surface of an object or organism. In nature, this can be seen in various forms, such as the skin of animals, the bark of trees, or the shell of eggs. The outer layer serves protective functions, shielding the inner components from environmental factors like moisture, temperature changes, and physical damage. In materials science, the outer layer can refer to coatings applied to surfaces for protection or aesthetic purposes. For example, paint on a wall or a sealant on wood provides a barrier against wear and tear. These outer layers enhance durability and can improve the appearance of the underlying material.