A Beautiful Planet calls Earth's atmosphere "a delicate cocoon of air that shields us from our star's radiation." Of course, the atmosphere doesn't completely block electromagnetic radiation from the Sun; without some sunlight reaching the surface, plants could not harvest the Sun's energy, and practically no life as we know it could exist. The atmosphere's ozone layer does filter out much of the harmful ultraviolet light (or "UV rays") produced by the Sun. UV rays can cause skin cancer, and catastrophic damage to the ozone layer may have contributed to Earth's most extensive mass extinction of species ever, the End-Permian extinction (also known
Ultraviolet index Ultraviolet index The ultraviolet index or UV Index is an international standard measurement of the strength of sunburn-producing ultraviolet (UV) radiation at a particular place and time. The scale was developed by Canadian scientists in 1992, then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994. It is primarily used in daily forecasts aimed at the general public, and is increasingly available as an hourly forecast as well. The UV Index is designed as an open-ended linear scale, directly proportional to the intensity of UV radiation that causes sunburn on human skin. For example,