Carbon 12 carbon dating
Carbon 14 is formed in the atmosphere when cosmic rays interact with nitrogen.
Obviously, this works only for things which were once living.
Carbon 14 is radioactive, meaning that the nucleus is unstable with the extra neutrons.
Eventually a carbon 14 atom will emit an electron and decay into an atom of nitrogen 14. Living organisms exchange all isotopes of carbon with the environment as it it passed along the food chain.
Before we get into the details of how radiometric dating methods are used, we need to review some preliminary concepts from chemistry.
Recall that atoms are the basic building blocks of matter.