How they do this will be discussed below with the effects of radiation on human tissues. Background or natural sources and doses Because cosmic radiation comes from outer space, the amount of radiation is greater at higher levels in the atmosphere. Therefore, a person who lives at a high level of elevation above sea level will receive more cosmic radiation exposure. Radioactive materials occurring naturally on earth in soils and rocks emit radiation. Someone living in a stone house would receive more radiation than a person who lived in a wooden house.
Granite is an example of a rock with a high proportion of radioactivity.
Most radiation exposure from natural rocks and minerals is usually much lower. However, since 1984, a natural radiation source called radon has been causing great concern in parts of the United States and Europe. Radon is a colorless, odorless, radioactive gas that seeps up from uranium deposits in the ground into houses and other buildings. The U. S. Environmental Protection Agency considers it the second largest cause of lung cancer after cigarette smoking and calls it an environmental problem of enormous proportions, far more so, it said at the time this review was written, than the radiation emitted from nuclear power plants. Officials believe that the radon problem is a world-wide one and that other nations will shortly find it affecting their populations.