Radon is a decay product of radium, which in turn is a decay product of uranium.
Rocks break down mechanically and chemically to form sediments that contain differing amounts of uranium, depending on the source rocks. The higher the uranium concentration is in the source rocks, the greater the chances are for radon in the air, soil, or ground water. Other potential sources of uranium in the environment are improper disposal of uranium mining waste and nuclear fuel processing, combustion of wood and fossil fuels, or roasting of rocks in metal extraction or cement industries. Radon in ground water affects radon concentrations in indoor air in homes because it escapes to the indoor air as people use water. Open water-distribution systems allow ground water to aerate and radon to escape.