True or False: All radioactivity is man-made.

It's a commonly held misconception that there are no natural sources of radiation. Nevertheless, it is present almost everywhere. Terrestrial radiation is found in areas with mineralized sand; cosmic one is received by the people who live at high altitudes. We breathe in the air loaded with radon - radioactive gas which comes from the Earth's interior. So, natural radiation is found in soil, atmosphere, space and even in the human body. Besides, in most cases our body receives natural radioactive nuclides from the food we eat!