Uv Light

http://science.hq.nasa.gov/kids/imagers/ems/uv.html


"Though some ultraviolet waves from the Sun penetrate Earth's atmosphere, most of them are blocked from entering by various gases like Ozone. Some days, more ultraviolet waves get through our atmosphere. Scientists have developed a UV index to help people protect themselves from these harmful ultraviolet waves."

http://www.sciencedaily.com/releases/2005/05/050503153444.htm

Carnegie Institution (2005, May 3). Rock Hounds Sleuth Rise Of Earth's Atmosphere. ScienceDaily. Retrieved May 28, 2008, from http://www.sciencedaily.com­ /releases/2005/05/050503153444.htm

"The detective work involves a pantheon of scientists who have analyzed surface minerals from all over the globe, used rockets and balloons to sample the stratosphere, collected and studied ice cores from Antarctica, conducted lab experiments, and run mathematical models. The synthesis from the different fields and techniques points to ultraviolet (UV) light from the Sun as an important driving force in atmospheric evolution. Solar UV photons break up molecular oxygen (O2) to produced ozone (O3) leaving a tell-tale isotopic signature of excess 17O. The ozone layer began to form as the atmosphere gained oxygen, and has since shielded our planet from harmful solar rays and made life possible on Earth's surface."