Carbon dating half lives
This technique is not restricted to bones; it can also be used on cloth, wood and plant fibers. The short half-life of carbon-14 means its cannot be used to date extremely old fossils.
Carbon-14 dating has been used successfully on the Dead Sea Scrolls, Minoan ruins and tombs of the pharohs among other things. Levels of carbon-14 become difficult to measure and compare after about 50,000 years (between 8 and 9 half lives; where 1% of the original carbon-14 remains undecayed).
Nitrogen normally occurs in a seven proton, seven nuetron, nitrogen-14 state.
Carbon-14 formed in the atmosphere can combine with oxygen to form carbon dioxide (CO2).
Carbon-14 in the bodies of animals and plants is constantly decaying.
However, the decaying carbon-14 is constantly being replaced as the plant or animal consumes more carbon-14 from the air or through its food.
Nuclear tests, nuclear reactors and the use of nuclear weapons have also changed the composition of radioisotopes in the air over the last few decades.
This human nuclear activity will make precise dating of fossils from our lifetime very difficult due to contamination of the normal radioisotope composition of the earth with addition artificially produced radioactive atoms.