Radioactivity is present everywhere - there is nothing that is not naturally slightly radioactive
We are not aware of this because our senses cannot detect radiation. Natural radioactive substances were originally formed in exploding stars (supernovae) and then incorporated into the earth. Their decay makes a significant contribution to geothermal heat. Natural radioactive substances also form to a small extent today through interaction with cosmic radiation in the atmosphere.
In Switzerland, we receive an average annual radiation dose of 5.5 millisieverts, mainly from natural sources. Some of the natural radiation comes from rock and soil, with the dose varying depending on location. Cosmic radiation is dependent on the altitude at which we live. The highest dose from natural sources comes from gaseous radon in our homes; this is released partly from construction materials and mainly from the underground environment.
We are also exposed to artificial radiation that differs from natural radiation in terms of its origin but not its properties and effects. Higher doses are caused by medical applications and much lower doses due to industrial applications.