Creationists also attack radioactive dating with the argument that half-lives were different in the past than they are at present. There is no more reason to believe that than to believe that at some time in the past iron did not rust and wood did not burn. Furthermore, astronomical data show that radioactive half-lives in elements in stars billions of light years away is the same as presently measured. On pages and of The Genesis Flood, creationist authors Whitcomb and Morris present an argument to try to convince the reader that ages of mineral specimens determined by radioactivity measurements are much greater than the "true" i.
The mathematical procedures employed are totally inconsistent with reality.
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Henry Morris has a PhD in Hydraulic Engineering, so it would seem that he would know better than to author such nonsense. Apparently, he did know better, because he qualifies the exposition in a footnote stating:. This discussion is not meant to be an exact exposition of radiogenic age computation; the relation is mathematically more complicated than the direct proportion assumed for the illustration.
Nevertheless, the principles described are substantially applicable to the actual relationship. Morris states that the production rate of an element formed by radioactive decay is constant with time. This is not true, although for a short period of time compared to the length of the half life the change in production rate may be very small. Radioactive elements decay by half-lives. At the end of the first half life, only half of the radioactive element remains, and therefore the production rate of the element formed by radioactive decay will be only half of what it was at the beginning.
The authors state on p. If these elements existed also as the result of direct creation, it is reasonable to assume that they existed in these same proportions. Say, then, that their initial amounts are represented by quantities of A and cA respectively. Morris makes a number of unsupported assumptions: This is not correct; radioactive elements decay by half lives, as explained in the first paragraphs of this post. There is absolutely no evidence to support this assumption, and a great deal of evidence that electromagnetic radiation does not affect the rate of decay of terrestrial radioactive elements.
He sums it up with the equations: He then calculates an "age" for the first element by dividing its quantity by its decay rate, R; and an "age" for the second element by dividing its quantity by its decay rate, cR. It's obvious from the above two equations that the result shows the same age for both elements, which is: Of course, the mathematics are completely wrong.
The correct relation can obtained by rearranging the equation given at the beginning of this post: For a half life of years, the following table shows the fraction remaining for various time periods:. By way of contrast, the following table displays the incorrect values calculated on the basis of the Morris straight line relationship: In all his mathematics, R is taken as a constant value. We may therefore set R as equal to the initial rate in the above table:. Calculating, using the Morris equation: Morris' equations would indicate that after years the amount of parent element would be completely gone, but the daughter element would nevertheless continue to be formed!
Click on the web site of Dr. Roger Wiens of Cal Tech for a detailed analysis of the accuracy of radioactive dating. Additional information is also available in talk. This half life is a relatively small number, which means that carbon 14 dating is not particularly helpful for very recent deaths and deaths more than 50, years ago. After 5, years, the amount of carbon 14 left in the body is half of the original amount. If the amount of carbon 14 is halved every 5, years, it will not take very long to reach an amount that is too small to analyze.
When finding the age of an organic organism we need to consider the half-life of carbon 14 as well as the rate of decay, which is —0. How old is the fossil? We can use a formula for carbon 14 dating to find the answer. The method was developed in the late s by Willard Libby , who received the Nobel Prize in Chemistry for his work in It is based on the fact that radiocarbon 14 C is constantly being created in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen.
The resulting 14 C combines with atmospheric oxygen to form radioactive carbon dioxide , which is incorporated into plants by photosynthesis ; animals then acquire 14 C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and from that point onwards the amount of 14 C it contains begins to decrease as the 14 C undergoes radioactive decay.
Measuring the amount of 14 C in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died. The older a sample is, the less 14 C there is to be detected, and because the half-life of 14 C the period of time after which half of a given sample will have decayed is about 5, years, the oldest dates that can be reliably measured by this process date to around 50, years ago, although special preparation methods occasionally permit accurate analysis of older samples.
Research has been ongoing since the s to determine what the proportion of 14 C in the atmosphere has been over the past fifty thousand years. The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age. Other corrections must be made to account for the proportion of 14 C in different types of organisms fractionation , and the varying levels of 14 C throughout the biosphere reservoir effects.
Additional complications come from the burning of fossil fuels such as coal and oil, and from the above-ground nuclear tests done in the s and s. Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its 14 C to decay below detectable levels, fossil fuels contain almost no 14 C , and as a result there was a noticeable drop in the proportion of 14 C in the atmosphere beginning in the late 19th century.
Conversely, nuclear testing increased the amount of 14 C in the atmosphere, which attained a maximum in about of almost twice what it had been before the testing began. Measurement of radiocarbon was originally done by beta-counting devices, which counted the amount of beta radiation emitted by decaying 14 C atoms in a sample.
More recently, accelerator mass spectrometry has become the method of choice; it counts all the 14 C atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples as small as individual plant seeds , and gives results much more quickly. The development of radiocarbon dating has had a profound impact on archaeology. In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances.
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Histories of archaeology often refer to its impact as the "radiocarbon revolution". Radiocarbon dating has allowed key transitions in prehistory to be dated, such as the end of the last ice age , and the beginning of the Neolithic and Bronze Age in different regions. In , Martin Kamen and Samuel Ruben of the Radiation Laboratory at Berkeley began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research.
They synthesized 14 C using the laboratory's cyclotron accelerator and soon discovered that the atom's half-life was far longer than had been previously thought. Korff , then employed at the Franklin Institute in Philadelphia , that the interaction of thermal neutrons with 14 N in the upper atmosphere would create 14 C. In , Libby moved to the University of Chicago where he began his work on radiocarbon dating. He published a paper in in which he proposed that the carbon in living matter might include 14 C as well as non-radioactive carbon. By contrast, methane created from petroleum showed no radiocarbon activity because of its age.
The results were summarized in a paper in Science in , in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin. Libby and James Arnold proceeded to test the radiocarbon dating theory by analyzing samples with known ages. For example, two samples taken from the tombs of two Egyptian kings, Zoser and Sneferu , independently dated to BC plus or minus 75 years, were dated by radiocarbon measurement to an average of BC plus or minus years.
These results were published in Science in In nature, carbon exists as two stable, nonradioactive isotopes: The half-life of 14 C the time it takes for half of a given amount of 14 C to decay is about 5, years, so its concentration in the atmosphere might be expected to reduce over thousands of years, but 14 C is constantly being produced in the lower stratosphere and upper troposphere , primarily by galactic cosmic rays , and to a lesser degree by solar cosmic rays. Once produced, the 14 C quickly combines with the oxygen in the atmosphere to form first carbon monoxide CO , [14] and ultimately carbon dioxide CO 2.
Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis. Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere. The ratio of 14 C to 12 C is approximately 1. The equation for the radioactive decay of 14 C is: During its life, a plant or animal is in equilibrium with its surroundings by exchanging carbon either with the atmosphere, or through its diet.
It will therefore have the same proportion of 14 C as the atmosphere, or in the case of marine animals or plants, with the ocean. Once it dies, it ceases to acquire 14 C , but the 14 C within its biological material at that time will continue to decay, and so the ratio of 14 C to 12 C in its remains will gradually decrease.
Radiometric dating
The equation governing the decay of a radioactive isotope is: Measurement of N , the number of 14 C atoms currently in the sample, allows the calculation of t , the age of the sample, using the equation above. The above calculations make several assumptions, such as that the level of 14 C in the atmosphere has remained constant over time. The calculations involve several steps and include an intermediate value called the "radiocarbon age", which is the age in "radiocarbon years" of the sample: Calculating radiocarbon ages also requires the value of the half-life for 14 C. Radiocarbon ages are still calculated using this half-life, and are known as "Conventional Radiocarbon Age".
Since the calibration curve IntCal also reports past atmospheric 14 C concentration using this conventional age, any conventional ages calibrated against the IntCal curve will produce a correct calibrated age. When a date is quoted, the reader should be aware that if it is an uncalibrated date a term used for dates given in radiocarbon years it may differ substantially from the best estimate of the actual calendar date, both because it uses the wrong value for the half-life of 14 C , and because no correction calibration has been applied for the historical variation of 14 C in the atmosphere over time.
Carbon is distributed throughout the atmosphere, the biosphere, and the oceans; these are referred to collectively as the carbon exchange reservoir, [32] and each component is also referred to individually as a carbon exchange reservoir.
How Carbon-14 Dating Works
The different elements of the carbon exchange reservoir vary in how much carbon they store, and in how long it takes for the 14 C generated by cosmic rays to fully mix with them. This affects the ratio of 14 C to 12 C in the different reservoirs, and hence the radiocarbon ages of samples that originated in each reservoir. There are several other possible sources of error that need to be considered. The errors are of four general types:. To verify the accuracy of the method, several artefacts that were datable by other techniques were tested; the results of the testing were in reasonable agreement with the true ages of the objects.
Over time, however, discrepancies began to appear between the known chronology for the oldest Egyptian dynasties and the radiocarbon dates of Egyptian artefacts. The question was resolved by the study of tree rings: Coal and oil began to be burned in large quantities during the 19th century. Dating an object from the early 20th century hence gives an apparent date older than the true date. For the same reason, 14 C concentrations in the neighbourhood of large cities are lower than the atmospheric average.
This fossil fuel effect also known as the Suess effect, after Hans Suess, who first reported it in would only amount to a reduction of 0. A much larger effect comes from above-ground nuclear testing, which released large numbers of neutrons and created 14 C. From about until , when atmospheric nuclear testing was banned, it is estimated that several tonnes of 14 C were created.
The level has since dropped, as this bomb pulse or "bomb carbon" as it is sometimes called percolates into the rest of the reservoir. Photosynthesis is the primary process by which carbon moves from the atmosphere into living things.
In photosynthetic pathways 12 C is absorbed slightly more easily than 13 C , which in turn is more easily absorbed than 14 C. This effect is known as isotopic fractionation. At higher temperatures, CO 2 has poor solubility in water, which means there is less CO 2 available for the photosynthetic reactions. The enrichment of bone 13 C also implies that excreted material is depleted in 13 C relative to the diet.