Prolonged exposure to the Sun causes sunburn, which over many years can develop into skin cancer. UV rays can also damage eyesight. UV rays are also harmful to other forms of wildlife, particularly small plants and animals living in the sea called plankton. Plankton are not protected from the Sun's rays, which can penetrate water to a depth of many metres. Plankton form the base of the ocean food chain. UV rays can damage certain crops, like rice, which many people in the world rely on for food. Finally, UV rays can damage paint, clothing and other materials. Any decrease in the amount of ozone in the ozone layer will increase the amount of UV rays reaching the Earth's surface, and worsen the impacts due to UV exposure.