Carbon-14 is radioactive, with a half-life of about 5,700 years.For more information on cosmic rays and half-life, as well as the process of radioactive decay, see How Nuclear Radiation Works.
When the neutron collides, a nitrogen-14 (seven protons, seven neutrons) atom turns into a carbon-14 atom (six protons, eight neutrons) and a hydrogen atom (one proton, zero neutrons).
If we knew the fraction of a radioactive element still remaining in a mineral, it would be a simple matter to calculate its age by the formula To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed.
Contrary to creationist claims, it is possible to make that determination, as the following will explain: By way of background, all atoms of a given element have the same number of protons in the nucleus; however, the number of neutrons in the nucleus can vary.
If a fossil contains 60% of its original carbon, how old is the fossil? That means this is how long it takes for half the nuclei to decay.
After 5600 years, if we start with a gram, we end up with half a gram.