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
Simple Model of the Atmospheric Radiative Transfer of Sunshine (for diffuse or global radiation) at any instant. Besides the atmospheric conditions, another important input is the solar geometry, which can be defined by the sun position (zenith angle and azimuth), the air mass, or by specifying the date, time and location. Optional calculations include the circumsolar irradiance, illuminance components, photosynthetically active radiation (PAR) components, and irradiance calculations in the UV, involving a variety of action spectra (such as that corresponding to the erythema). The program outputs its results to text files, which can be further imported and processed into spreadsheets. A graphic interface, providing plots of the calculated spectra