C 14 dating can be used on
Radioactive decay may be used in carbon dating, testing for the amounts of a radioactive carbon isotope (C14) in the remains of some organism. When the thing dies it no longer takes in carbon from the atmosphere through processes such as eating or respiration and levels of C14 in the body deplete due to the natural process of radioactive decay. Carbon-14 is naturally found in the atmosphere in the form of heavy CO2.
C14 obviously only works on organic material which was once alive, such as wood or bone. By seeing how much C14 remains it is possible to see how long it has been since… The reason for this has to do with neutron flux from the sun hitting nitrogen in the upper atmosphere - whatever.
Obviously this circulation stops when a C14 molecule gets incorporated into a plant or something that ate the plant. This is a very useful isotope for measuring archaeological material, and with a good sample, one may date a sample to about ten half lives - about 57300 years. The uncertainty of the measurement increases with the total time. The atmosphere consists of a certain ratio of carbon 14 to carbon 12. If you add a neutron you get c13 which is also stable.
Over time the C14 in a tree disappears while C14 in the iar keeps gettin renewed. C14 is not useful for recent dating because of the quantity of material released during atomic bomb testing. Although this ratio has been in decline since the dawn of the industrial revolution, when humans began pumping depleted CO2 into the atmosphere (fossil carbon contains virtually no C14), the ratio is sufficiently constant that accurate ages can be obtained from any organic material within ten half lives of C14. However one more neutron gives you C14 which is unstable. C14 is a very useful element in determining the age of younger fossils, up to 60-70,000 years old. Radioisotopes decay at a rate specific to the particular element (and its isotope).
The less radioactive decay ammount there is the older it is.
This would be the estimated age of the earliest life or formation of fossils. Uranium 238 is only found in igneous or volcanic rocks. Because of the huge differences in the half lives of Carbon 14 and Uranium238 they cannot be used together.
Carbon 14 can only be used to date fossils of a very recent age.
So, at the time of death, the C14 : C12 ratio is fixed.
C14 undergoes radioactive decay (into C12) so the C14 : C12 ratio declines and that can be used as a measure of the time since death. Carbon 14 (C14) is created in the upper atmosphere by the action of cosmic rays on Nitrogen atoms.