C-14 is formed in the earth’s upper atmosphere as a consequence of cosmic radiation bombardment.These cosmic rays shatter the nuclei in gas atoms in the upper atmosphere releasing neutrons.The fact is, carbon dating can only be used to date things up to approximately 50,000 years old.In fact, if an object contains (radioactive) carbon, this should be a clue that the object may not be any older than 50,000 years.
Carbon dating can only be used to date objects that were once living or even apart of a living organism. It cannot be used to directly date inorganic objects, such as rocks (other radioactive dating methods are used to date radioactive rocks).
Most authorities agree that C-14 decays at such a rate that half of it will be gone in approximately 5,730 years.
This means if a specimen contained, say, a pound of C-14 (to make things understandable), in 5,730 years, half of it will be gone, and in another 5,730 years, half of the remaining C-14 will disappear.
The displaced neutrons bond with nitrogen-14 (N-14) converting it into C-14.
Because C-14 is radioactive, it is unstable, and is constantly decaying back into N-14.