Most everyone has heard of Carbon dating on the news or elsewhere sometime in the past years. In this article I hope to explain the theoretical and physical science behind Carbon dating, and discuss how it affects our lives and the validity of the process. Scientists use Carbon dating for telling the age of an old object, whose origin and age cannot be determined exactly by normal means. Because of this method Chemistry has become intertwined with History, Archeology, Anthropology, and Geology.
Poole Many items that have been thought to come from one time have been tested and found out to actually come from a thousands years beforehand. Places where historians believed that human civilization came to exit say, only 2, years ago, have actually been proven to have had some form of human civilization more than 4, years ago.
Poole Fine art collectors have used Carbon dating to determine if a piece of antique art is actually genuine. Some have saved themselves several thousands of dollars by testing the piece before they bought it and finding out that it is not the original, but a very clever modern copy. Poole But how is this done? What are the ides behind carbon dating?
Atoms of given elements have different Isotopes. Isotopes are atoms of the same element, i. The element Carbon is in all living things, it is a basic building block for the construction of organic material. The normal molar mass of Carbon is around 12, however there are a few Carbon atoms that have a molar mass of about 13, and even fewer that have a molar mass of about These atoms have one or two more neutrons in the nucleus than most Carbon atoms.
Scientists call the isotope with molar mass around 14, Carbon Carbon is manufactured in the upper atmosphere by the action of cosmic rays. It turns out to be radioactive and decays over time. All organic material has decaying Carbon in it. However, plants and animals that are still alive constantly replace the supply of carbon in their systems and so the amount of Carbon in the system stays almost constant. Once a plant or animal dies the Carbon is no longer being regenerated and so the Carbon starts to decay.
In this way, by measuring the amount of Carbon in the body of a prehistoric animal or plant, a scientist can deduce when the plant or animal died. All radioactive materials have a half-life. If you have a certain amount of a radioactive material, its half-life is the time it takes for half of the material you started out with to decay. Carbon decays back into nitrogen. This is a first order reaction equation and the rate at which it the reaction proceeds what can you use carbon dating on time can be modeled by the equations: A reaction with a large rate constant has a short half-life.
Libby Was the man who first developed the idea and procedure for Carbon dating. He measured the half-life of Carbon to be about 5, years. However after about 50, years there is so little Carbon left in the specimen that it is very hard, almost impossible, to calculate its age. Van Der Merwe Libby ran many tests on items where the age was known, or estimated by other means. His test results came rather close, to within plus or minus a few hundred years.
In the laboratory, samples must be processed and cleaned so that there is no material on them that might throw off the age reading. Then the sample is burned and passes through a completely sterile vacuum system as Carbon dioxide gas. The gas is then subjected to more purifying procedures. Afterward the gas is stored in a tube insulated by Mercury and Lead, so as to minimize the chances of the what can you use carbon dating on being affected by radiations from the atmosphere. When a Carbon atom disintegrates fine instruments detect the action, a light flashes on a control panel, and a counter records what can you use carbon dating on number of decaying atoms.
By this method the scientist can keep track of how many atoms are decomposing per minute and per second. We are now ably to date anything we want, even that something at the back of the fridge, and know how old it is within a few hundred years, but are there any problems with the Carbon dating method? In order to know how long a sample of radioactive material had been decomposing we need three variables defined, how much of the sample we have left now, what the half-life of the sample is, and how much of the sample we started out with.
For Carbon dating we have already experimentally measured the amount of Carbon left, and Libby has already measured the half-life of Carbon to an acceptable exactness, however how much Carbon was there in the specimen at the time of death. The amount of Carbon in an organic body is constant with the amount what can you use carbon dating on Carbon in the atmosphere. Thus specimens have the same amount of carbon in them as the rest of the atmosphere at the time that the specimen lived.
However, if we could measure the amount of Carbon in the atmosphere when they lived, we would be living during the time and there would be no reason for dating. We know for a fact that the amount of Carbon in the atmosphere has not stayed the same in the past century. A recent proof of that would be the Industrial revolution. Factories put out massive amounts of Carbon, and during that time the concentration of Carbon in the atmosphere increased significantly. Fortunately, Libby was a smart guy and accounted for this discrepancy.
He measured the amount of Carbon in the inner layers of trees that were older than the Industrial revolution. He was able to calculate the amount of Carbon in the atmosphere, before the industrial revolution, and adjust his equation accordingly. However, Libby then assumed that the amount of Carbon in the atmosphere was relatively constant for a very long time up until the Industrial revolution. Can this be assumed to be correct? In the atmosphere the amount of Carbon decaying over time increases with the greater concentration of Carbon in the atmosphere.
Eventually the reaction would reach some equilibrium and the amount of Carbon in the atmosphere would remain constant. Scientists have calculated that the amount Carbon in the atmosphere would become stable after 30, years from the beginning of the reaction.