How Carbon Dating Works, Easy explanation

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This will clear up the confusion on Carbon dating. Carbon has unique properties that are essential for life on earth. Familiar to us as the black substance in charred wood, as diamonds, and the graphite in ‘lead’ pencils, carbon comes in several forms, or isotopes. One rare form has atoms that are 14 times as heavy as hydrogen atoms: carbon-14, or 14C, or radiocarbon. Carbon-14 is made when cosmic rays knock neutrons out of atomic nuclei in the upper atmosphere. These displaced neutrons, now moving fast, hit ordinary nitrogen (14N) at lower altitudes, converting it into 14C. Unlike common carbon (12C), 14C is unstable and slowly decays, changing it back to nitrogen and releasing energy. This instability makes it radioactive. Ordinary carbon (12C) is found in the carbon dioxide (CO2) in the air, which is taken up by plants, which in turn are eaten by animals. So a bone, or a leaf or a tree, or even a piece of wooden furniture, contains carbon. When the 14C has been formed, like ordinary carbon (12C), it combines with oxygen to give carbon dioxide (14CO2), and so it also gets cycled through the cells of plants and animals. We can take a sample of air, count how many 12C atoms there are for every 14C atom, and calculate the 14C/12C ratio. Because 14C is so well mixed up with 12C, we expect to find that this ratio is the same if we sample a leaf from a tree, or a part of your body. In living things, although 14C atoms are constantly changing back to 14N, they are still exchanging carbon with their surroundings, so the mixture remains about the same as in the atmosphere. However, as soon as a plant or animal dies, the 14C atoms which decay are no longer replaced, so the amount of 14C in that once-living thing decreases as time goes on. In other words, the 14C/12C ratio gets smaller. So, we have a ‘clock’ which starts ticking the moment something dies. Obviously, this works only for things which were once living. It cannot be used to date volcanic rocks, for example. The rate of decay of 14C is such that half of an amount will convert back to 14N in 5,730 years (plus or minus 40 years). This is the ‘half-life.’ So, in two half-lives, or 11,460 years, only one-quarter will be left. Thus, if the amount of 14C relative to 12C in a sample is one-quarter of that in living organisms at present, then it has a theoretical age of 11,460 years. Anything over about 50,000 years old, should theoretically have no detectable 14C left. That is why radiocarbon dating cannot give millions of years. In fact, if a sample contains 14C, it is good evidence that it is not millions of years old. However, things are not quite so simple. First, plants discriminate against carbon dioxide containing 14C. That is, they take up less than would be expected and so they test older than they really are. Furthermore, different types of plants discriminate differently. This also has to be corrected for.2 Second, the ratio of 14C/12C in the atmosphere has not been constant—for example, it was higher before the industrial era when the massive burning of fossil fuels released a lot of carbon dioxide that was depleted in 14C. This would make things which died at that time appear older in terms of carbon dating. Then there was a rise in 14CO2 with the advent of atmospheric testing of atomic bombs in the 1950s.3 This would make things carbon-dated from that time appear younger than their true age. Measurement of 14C in historically dated objects (e.g., seeds in the graves of historically dated tombs) enables the level of 14C in the atmosphere at that time to be estimated, and so partial calibration of the ‘clock’ is possible. Accordingly, carbon dating carefully applied to items from historical times can be useful. However, even with such historical calibration, archaeologists do not regard 14C dates as absolute because of frequent anomalies. They rely more on dating methods that link into historical records. Outside the range of recorded history, calibration of the 14C clock is not possible. For more info see http://www.answersingenesis.org/