RE:RE:event On Radon, form Wikipedia:
'Radon is a
chemical element with symbol
Rn and
atomic number 86. It is a
radioactive, colorless, odorless, tasteless
[2]noble gas, occurring naturally as an indirect
decay product of
uranium or
thorium.
… Radon is formed as one intermediate step in the normal radioactive
decay chains through which thorium and uranium slowly decay into
lead. Thorium and uranium are the two most common radioactive elements on earth; they have been around since the earth was formed. Their naturally occurring isotopes have very long half-lives, on the order of billions of years. Thorium and uranium, their decay product
radium, and its decay product radon, will therefore continue to occur for tens of millions of years at almost the same concentrations as they do now. ...'