“ch a impact on the thinking of so many fields of human endeavor. Seldom has a single discovery generated such wide public interest.
“From Taylor, 1987The radiocarbon dating process was developed by physicist Willard F. Libby (please see photo) in 1948 with the help of two scientists, Dr. E. C. Anderson and Dr.
James R. Arnold. Libby was born on December 17, 1908 in Grand Valley, Colorado. He taught at the University of California-Berkeley from 1933-1941. In 1941 Libby began working on the Manhattan Project, a top secret project supported by the United States government.
The purpose of the Manhattan Project was to develop an atomic bomb. The scientists involved in the project succeeded and their efforts directly correlated to the end of WWII. Libbys discovery of radiocarbon coincidentally took place at the University of Chicago, the same place where the beginnings of the atom bomb occurred. Both the atom bomb and radiocarbon dating influence the field of science even today.
In 1960 Libby won the Nobel Prize in Chemistry, “for his method to use Carbon-14 for age determinations in archaeology, geology, and other bran!ches of science. ” Libby died in 1980. Radiocarbon dating is a technique in which scientists can answer many questions about the past in the fields of archaeology, anthropology, atmospheric science, biomedicine, climatology, geology, oceanography, and palaeoclimatology. Scientists, with the help of the radiocarbon dating process, are able to date objects such as skeletons, fossils, and ancient artifacts like pottery and tools.
The dates of these objects allow scientists to show how long ago a civilization (i. e. Incans, Sumerians, etc. ) lived, how old something is, and ultimately, is the bible correct.
A normal carbon atom, Carbon-12, has six protons, six neutrons, and six electrons. A Carbon-14 isotope is extremely unstable, and therefore, radioactive. Carbon-12 accounts for 98. 89% of all carbon present.
Carbon-13 accounts for 1. 11% and C-14, radiocarbon is . 0000000010% of all carbon in the world. From these numbers, it can be determined that for every atom of Carbon-14, there are1,000,000,000,000 Carbon-12 atoms out there. Carbon-14 has two extra neutrons, brining its neutron total to eight.
Carbon-14 returns to its stable form of Carbon-12 through a process of decay. The radiocarbon process is based on the rate of decay of the unstable Carbon-14 isotope. Carbon-14 is formed in the upper atmosphere of the earth when cosmic rays and Nirogen-14 interact. The reaction is:14N+n=>14C+p(where n is a neutron and p is a proton)Scientists believe that these cosmic rays have been bombarding the earths upper atmosphere since the beginning of time, while the amount of nitrogen in the earths upper atmosphere has remained constant as well. The formation of Carbon-14 is thought to occur at a constant rate.
Thus, for Carbon-14 to have occurred at a constant rate since the beginning of time, so must have the amount of cosmic rays and nitrogen in the earths atmosphere. The current ratio of Carbon-14 to other forms of carbon is known, though scientists are not sure whether that ratio has been the same for all of time. The do, however, say that the radiocarbon process is accurate in dating objects back to at least 50,000 years. The Carbon-14 formed in the upper atmosphere of the earth is rapidly oxidized into 14CO2 and then is able to enter the earths plant and animal life through the process of photosynthesis, by way of the food chain, and also enters the earths oceans in an atmospheric exchange and as a dissolved carbonate. This rapid dispersal of Carbon-14 into the earths atmosphere has been demonstrated by measurements of radioactive carbon that has been produced from thermonuclear bomb testing. Plants and animals, which utilize carbon in biological food chains, will at one time or another, take up Carbon-14.
When this plant or animal dies, there is no more intake of Carbon-14, or any other substance for that matter. This is when the process of carbon dating begins. Libby and other scientists discovered that the decay of Carbon-14 occurs at a constant rate. The half-life of Carbon-14, they said, was 5,568+/-30 years. This is known as the Libby half-life.
If, for example, a brontosaurus died, half of its Carbon-14 would be gone 5,568 years after his death. Leaving him with 50% of its original total. Another 5,568 years after that, half of his previous total would be left, leaving it with a total of 25% of that when it was alive. This process can, and will continue forever, because the brontosaurus will always have some of the carbon left, even if it is a very minute amount. After ten half-lives, however, there is a very small amount of radioactive material left. At about 50,000-60,000 years, the limit of radiocarbon dating has been reached and the results will not be accurate.
By measuring the radioactivity of an object whose age is not known, it is possible to find the number of decay events per gram of carbon. By comparing an!object with modern levels of activity and using the half-life method, it becomes possible to calculate a date of death for the object. For example, if one was to measure the amount of Carbon-14 left in a tree that has long since been dead and whose time of death was unknown, and compared that measurement with the measurement one would get with the amount of Carbon-14 in a tree that had very recently died, they could date the dead tree. This is how one would go about finding the dates of death for objects. However, Libby and the other scientists did not take into account that the radiocarbon level in the atmosphere varied slightly over time. The true half-life of Carbon-14 is 5,730 years, not the original 5,568 that Libby and his team found.
Because the amount of radiocarbon in the atmosphere varied, that makes it necessary to calibrate the results of a radiocarbon dated sample. The calibration of the results is really quite simple, though. One can look through the tree ring record for a ring with the same proportional amount of Carbon-14 as is present on the sample. Since the calendar age of the tree is known, one can tell how old their sample is. Unfortunately, this relatively simple process is complicated by two factors.
First, the measurements of both the tree rings and the sample have a limited precision and thus, there will be a range of possible calendar years. Second, seeing as the atmospheric radiocarbon concentration has varied, it is feasible to believe that there may be, in fact, several ranges. This is why one must use a graph with known values of dates on it. This graph is not linear, if it were linear that would mean that the amount of radiocarbon in the atmosphere of the earth would have been constant. This is not so, thus, the graph jumps and dips at different dates in time. This graph is called the, calibration curve.
There are two main methods for calculating dates from the calibration curve. The first method is called the, “intercept method”. This is done by drawing lines on the graph that intercept the curve. This method will tell one the years that the radiocarbon concentration of tree rings is within two standard deviations of ones measurement. The second method is more often used and is called the “probability method”. It requires a computer because the calculations are very complicated.
This method gives a time range in which the examiner can be 95% sure that the sample came. There are a number of calibration programs on the market for anyone to use. The original DOS program, CALIB the Windows program OxCal are the most widely used. As Carbon-14 decays, it emits a weak beta particle, or electron, which has an average energy of 160keV. This is the reaction_14C=>14N+b(where b is the beta particle, or electron)The Carbon-14 changes back into the nitrogen.
The decay of the Carbon-14 atom is constant, but at the same time it happens spontaneously. The probability of decay for a Carbon-14 atom is constant, thereby requiring the application of statistical methods for the analysis of counting the data that was recorded. All radiocarbon measurements are recorded in terms of years, “before present,” or BP. This figure is based on the assumption that the proportion of radiocarbon in the atmosphere is the same as it was when it was measured in 1950. Whenever the word “present” is used, it is referring to 1950. I think that I shall never see, a sample of a plain old tree,a tree thats not been carved or painted, calcified, burned or otherwise tainted,But bones and shells and peat I get; preparing them all day I sweat.
Wont someone please take pity on me, and send in just one plain old tree. T. A. Rafter in Procs 6th International Radiocarbon Conference, Pullman, 1965. All trees lay down tree rings, but not all types of trees reliably lay down lay down one tree ring a year.
Only a few trees measurements of rings and radiocarbon in the atmosphere can be trusted. These rings can be used to record the radiocarbon concentrations of the past. If a tree is 350 years old, it would be possible to measure the amount of radiocarbon in the 350 rings and see which radiocarbon concentration corresponds to each calendar year. In the United States, the Great Basin Bristlecone Pine, mainly in the west, is one such reliable tree. The waterlogged oak trees of Germany and Ireland provide useful records for over the past 11,000 years. The true beauty of radiocarbon dating though, is that any material composed of carbon can be dated.
As one knows, carbon is present in everything that is or has at one time been alive. With that luxury, radiocarbon dating can be uniformly applied throughout the world. Currently there are over 130 radiocarbon dating laboratories around the world. These laboratories produce radiocarbon examinations and determinations for the scientific community. Not only the scientific community, but for anyone as well.
If one has enough money and wants to know how old an object is, they need only to take it to a radiocarbon dating laboratory. The United States, Russia, China, and Germany have far more radiocarbon dating laboratories than other countries. A significant amount of these laboratories are at colleges and universities, though some privately owned laboratories are trusted by scientists and people world-wide. The largest radiocarbon dating facility in the world is in Miami, Florida. Beta Analytic is the largest radiocarbon dating laboratory in the world.
It dates over 10,000 samples a year. Anyone can send a sample to be dated. All that is required, besides money, is that there be at least .03 grams of measurable carbon in the sample and, if the sample is sent
