Subscribe to our newsletter. Exposure A beginner's guide. Three Mile Island Yucca Mountain Radiation and radioactivity occur naturally in the physical world. All living beings require some kinds of radiation just to live. Light and heat, for example, are two basic forms of radiation necessary for all life on Earth.
Radiation is a form of energy.
Radioactivity is the spontaneous emission of energy from certain elements, and from other elements under special conditions, in the form of particles or electromagnetic waves. More than 80 percent of the radiation we are exposed to comes from such natural sources as sunlight, soil, and certain types of rocks. Cosmic rays filtering down through the atmosphere, and radon gas filtering up through the soil, are sources of natural radiation. This radiation is called background radiation. It is present everywhere, all the time and varies greatly depending on our geographical location.