Identify natural sources of background radiation, including rocks, cosmic rays, radon gas, food and living organisms.

Natural sources of background radiation include cosmic rays from outer space, which constantly bombard the Earth, and radiation emitted from rocks and soil, particularly those containing uranium and thorium. Radon gas, a radioactive gas that seeps from the ground, contributes significantly to background radiation levels, especially in enclosed spaces. Additionally, food and living organisms contain trace amounts of radioactive isotopes, contributing to the overall background radiation. Understanding these sources is crucial for assessing radiation exposure and its potential health effects.