Carbon 14 used carbon dating
This carbon-14 labeled carbon dioxide is taken up by plants in their normal process of photosynthesis.
Animals and people that eat these plants take the carbon-14 into their bodies as well.
Also, many fossils are contaminated with carbon from the environment during collection or preservation proceedures.
When scientists first began to compare carbon dating data to data from tree rings, they found carbon dating provided "too-young" estimates of artifact age.
Scientists now realize that production of carbon-14 has not been constant over the last 10,000 years, but has changed as the radiation from the sun has changed.
These isotopes have longer half-lives and so are found in greater abundance in older fossils.These artifacts have gone through many carbon-14 half-lives and the amount of carbon-14 remaining in them is miniscule and very difficult to detect.Carbon dating cannot be used on most fossils, not only because they are almost always too old, but also because they rarely contain the original carbon of the organism.These collisions create secondary cosmic rays in the form of energentic neutrons.When these neutrons collide with nitrogen-14 in the atmosphere carbon-14 can be created.