Carbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60000 years. Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere.
When neutrons collide, a nitrogen-14(seven protons, seven neutrons) atom turns into a carbon-14 atom (six protons, zero neutrons) and a hydrogen atom (one proton, zero neutrons. The radioactive carbon-14 combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.Carbon-14 is a radioactive with a half life of about 5700 years. The cost to date is very expensive. On average it is 250 US dollars
HOW CARBON-14 IS MADE
DATING A FOSSIL
OCURRENCE OF CARBON -14
THE OTHER THING BY WHICH DATING IS DONE USING RADIO CARBON
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UNCERTAINTY IN CARBON DATING
COST TO DATE RADIO CARBON
Carbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60000 years. The technique was developed by Willard Libby and his colleagues in 1949.during his tenure as a professor at the University of Chicago. Libby estimated that the radioactivity of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram. In 1960, he was awarded the Noble Prize in Chemistry for this work. One of the frequent uses of the technique is to date organic remains from archaeological sites. Plants fix atmospheric carbon during photosynthesis, so the level of 14C in plants and animals when they die approximately equals the level of 14C in the atmosphere at that time. However, it decreases thereafter from radioactive decay, allowing the date of death or fixation to be estimated. The initial 14C level for the calculation can either be estimated, or else directly compared with known year-by-year data from tree-ring data (dendochronology) to 10,000 years ago, or from cave deposits (speleothems), to about 45,000 years of age. A calculation or (more accurately) a direct comparison with tree ring or cave-deposit carbon-14 levels, gives the wood or animal sample age-from-formation. The technique has limitations within the modern industrial era, due to fossil fuel carbon (which has little carbon-14) being released into the atmosphere in large quantities, in the past few centuries. It is also used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities. Carbon-14 can be used as a radioactive tracer in medicine. In the initial variant of the urea breadth test, a diagnostic test for helicobacter pylori urea labeled with approximately 37Â kBq (1.0ÂµCi) carbon-14 is fed to a patient. In the event of a H. Pylori infection, the bacterial urease enzyme breaks down the urea into ammonia and radioactively-labeled carbon dioxide, which can be detected by low-level counting of the patient's breath. The 14-C urea breath test has been largely replaced by the 13-C urea breath test which has no radiation issues.
HOW CARBON -14 IS MADE
Carbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis.
Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere. When neutrons collide, a nitrogen-14(seven protons, seven neutrons) atom turns into a carbon-14 atom (six protons, zero neutrons) and a hydrogen atom (one proton, zero neutrons. The radioactive carbon-14 combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.Carbon-14 is a radioactive with a half life of about 5700 years.
The carbon-14 forms at a rate which appears to be constant, so that by measuring the radioactive emissions from once-living matter and comparing its activity with the equilibrium of living things, a measurement of the time elapsed can be made.
DATING A FOSSIL
Carbon dating is a dating technique predicated upon three things:
â€¢ The rate at which the unstable radioactive C-14 isotope decays into the stable non-radioactive N-14 isotope,
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â€¢ The ratio of C-12 to C-14 found in a given specimen,
â€¢ And the ratio C-12 to C-14 found in the atmosphere at the time of the specimen's death.
As soon as a living organism dies, it stops taking in new carbon.Thecarbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely.
A formula to calculate how old a sample is by carbon-14 dating is:
t= [ln (Nf/No) / (-0.693)] x t1/2
where ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years).
So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be:
t = [ln (0.10) / (-0.693)] x 5,700 years
t = [(-2.303) / (-0.693)] x 5,700 years
t = [3.323] x 5,700 years
t = 18,940 years old
Because the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years
OCURRENCE OF CARBON -14
IN FOSSIL FUELS:-
Most man-made chemicals are made of fossil fuels, such as petroleum or coal, in which the carbon-14 should have long since decayed. However, such deposits often contain trace amounts of carbon-14 (varying significantly, but ranging from 1% the ratio found in living organisms to amounts comparable to an apparent age of 40,000 years for oils with the highest levels of carbon-14). This may indicate possible contamination by small amounts of bacteria, underground sources of radiation (such as uranium decay, although reported measured ratios of 14C/U in uranium-bearing ores would imply roughly 1 uranium atom for every two carbon atoms in order to cause the 10âˆ’15 14C/12C measured), or other unknown secondary sources of carbon-14 production. Presence of carbon-14 in the isotropic signature of a sample of carbonaceous material possibly indicates its contamination by biogenic sources or the decay of radioactive material in surrounding geologic strata.
IN THE HUMAN BODY AND ANIMALS:-
Since essentially all sources of human food and animals are derived from plants, the carbon that comprises our bodies contains carbon-14 at the same concentration as the atmosphere. The beta-decays from this internal radiocarbon contribute approximately 0.01 mSv/year (1 mrem/year) to each person's dose of ionizing radiation. This is small compared to the doses from potassium-40(0.39 mSv/year) and radon.
Carbon-14 can be used as a radioactive tracer in medicine. In the initial variant of the urea breadth test, a diagnostic test for helicobacter pylori urea labeled with approximately 37Â kBq (1.0ÂµCi) carbon-14 is fed to a patient. In the event of a H.pylori infection, the bacterial urease enzyme breaks down the urea into ammonia and radioactively-labeled carbon dioxide, which can be detected by low-level counting of the patient's breath. The 14-C urea breath test has been largely replaced by the 13-C urea breath test which has no radiation issues.
IN SOLAR VARIATION:-
The number of particles shot out by the Sun varies with the eleven-year cycle of sunspots. Also, the Sun's own magnetic field varies with the cycle, and that could change the way cosmic particles bombarded the Earth. So carbon dating helps in determining different variation.
The carbon dating process is used in finding the age of old monuments, artifacts, archaeological excavation etc. Everything from mastodons to the Shroud of Turin has been dated using this technique.
Measuring the carbon content in the Pacific and Indian Ocean to understand better the processes of ocean circulation.
THE OTHER THINGS BY WHICH DATING IS DONE USING RADIO CARBON
Charcoal, wood, twigs and seeds.
Marine, estuarine and riverine shell.
Coprolites (samples of preserved feces).
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Lake mud's (gyttja) and sediments.
Metal casting ores.
Wall paintings and rock art works.
Iron and meteorites.
Corals and foraminifera.
Textiles and fabrics.
Paper and parchment.
Resins and glues.
Antler and horn.
UNCERTAINTY IN CARBON DATING
Carbon dating is controversial for a couple of reasons. First of all, it's predicated upon a set of questionable assumptions. We have to assume, for example, that the rate of decay (that is, a 5,730 year half-life) has remained constant throughout the unobservable past. However, there is strong evidence which suggests that radioactive decay may have been greatly accelerated in the unobservable past. We must also assume that the ratio of C-12 to C-14 in the atmosphere has remained constant throughout the unobservable past (so we can know what the ratio was at the time of the specimen's death). And yet we know that "radiocarbon is forming 28-37% faster than it is decaying,"2 which means it hasn't yet reached equilibrium, which means the ratio is higher today than it was in the unobservable past. We also know that the ratio decreased during the industrial revolution due to the dramatic increase of CO2 produced by factories. This man-made fluctuation wasn't a natural occurrence, but it demonstrates the fact that fluctuation is possible and that a period of natural upheaval upon the earth could greatly affect the ratio.
Volcanoes spew out CO2 which could just as effectively decrease the ratio. Specimens which lived and died during a period of intense volcanism would appear older than they really are if they were dated using this technique. The ratio can further be affected by C-14 production rates in the atmosphere, which in turn is affected by the amount of cosmic rays penetrating the earth's atmosphere. The amount of cosmic rays penetrating the earth's atmosphere is itself affected by things like the earth's magnetic field which deflects cosmic rays. Precise measurements taken over the last 140 years have shown a steady decay in the strength of the earth's magnetic field. This means there's been a steady increase in radiocarbon production (which would increase the ratio).
And finally, this dating scheme is controversial because the dates derived are often wildly inconsistent.
COST TO DATE RADIO CARBON
The cost varies between different laboratories. On average, a single date will cost about 250 US dollars. The high cost is because it is a big job to date a sample. It takes a long time to change the carbon material into the form it needs to be in to be able to be dated. As well as that, the equipment is very expensive and has ongoing costs associated with it. An AMS dating instrument for example, costs around $2-3 million dollars.
1. The key assumption of equilibrium is false.
2. Carbon dating is a reliable dating method for less than 3000 years and not the claimed 60000 years found in textbooks.