[mountainlion]

Half of the heat in the world comes form radioactive decay form deep in the earth. This is the most ignored source of heat.

[American Constitutionalist]

Radon : a chemical element with the atomic number 86, and is represented by the symbol Rn. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days.

Ain't nothing humans or the environmentalist can do about it, it happens naturally.