Dating with carbon 14
Above is a graph that illustrates the relationship between how much Carbon 14 is left in a sample and how old it is. The Carbon Dioxide released released by burning fossil fuels has too little Carbon-14 because coal, oil and natural gas contain very little Carbon-14 .
Carbon-14 on the other hand is an unstable isotope; that is, it decays naturally over time. It is produced naturally in the atmosphere and mixes with carbon-12 becoming part of our planet's biosphere.They have masses of 13 and 14 respectively and are referred to as "carbon-13" and "carbon-14." If two atoms have equal numbers of protons but differing numbers of neutrons, one is said to be an "isotope" of the other.Carbon-13 and carbon-14 are thus isotopes of carbon-12.As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged.