This book discusses UV radiation, its effects on ecosystems and the likely evolutionary consequences of changed UV radiation environments, past, present and future. The first two chapters examine the history of the UV radiation climate of earth and the factors that determine organismal and ecosystem exposure. Their purpose is to give the reader a physical perspective on UV radiation and an understanding of the constantly changing UV environment that ecosystems are exposed to over time. Variations in the UV radiation environment occur at the local level (such as boundary layer and plant canopy...