'Carbon dating', is it just guess work?

Question

There just seems to be too much room for error.

CD is still relevant, it's the best we have, but shouldn't be presented as fact.

Answer 1

No not at all.Carbon dating is the process in which one counts the amount of C14 atoms in a degrading body,from the time of death of the organism.It can be very precise to predict the age of any substance

Answer 2

OK...here's how it works:

Cosmic rays hitting atoms in the atmosphere cause nuclear fission, producing neutrons which bombard N 14-7 to produce C 14-6 and H 1-1. C-14 has a long half life and slowly reverts to N-14 by beta decay. The atmosphere contains a constant concentration of C-14 as 14-CO2, which enters into plants and animals via the carbon cycle. Thus all living things have a constant proportion of C-14 in their carbon content. However, when an animal or plant dies, replacement of carbon 14 stops but decay continues. By comparing the C-14 content of an archaeological sample with that of a similar living species, and allowing for changes in the atmospheric content of carbon-14 over the years, it is possible to estimate the age of the sample.

The calculation works out as follows:

C(t) = C(0)*e^(-k*t) ==> t = ln[C(t)/C(0)] / -k

where:
C(t) is the number of counts of C-14 in an archaelogical sample
C(0) is strictly speaking the number of counts of C-14 in the sample at the time of its death, but this is obviously difficult to measure, so a similar living species is taken, and its C-14 count is adjusted by looking at changes in atmospheric levels of C-14 over recent years.
k = degradation rate constant of C-14, which can be worked out as: k = ln 2 / t(0.5) where t(0.5) is the half-life of C-14, which is approximately 5690 years.

So...in answer to your question....yes...there is a little bit of approximation in carbon dating, because the calculations on how much C-14 was present in the atmosphere in prehistoric times and therefore how much C-14 was present in the body of a dinosaur when it died, are simply....approximations based on models.

Answer 3

Not at all.
It refers to the rate in which a certain isotope of carbon breaks down. It breaks down at a predictable rate. You know how old something is by measuring how much is left in the old thing.
It's expensive too.

Answer 4

u can say it as guess

carbon's radioactive isotope is taken to find out age of fossils it gives nearly about the exact time when the creature was dead { birth time cannot be find out}

Answer 5

Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of carbonaceous materials up to about 60,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" (BP), "Present" being defined as AD 1950. Such raw ages can be calibrated to give calendar dates.

The technique of radiocarbon dating was discovered by Willard Frank Libby and his colleagues in 1949 during his tenure as a professor at the University of Chicago. Libby estimated that the steady state radioactivity concentration of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram carbon (ca 230 mBq/g). In 1960, Libby was awarded the Nobel Prize in chemistry for his method to use carbon-14 (14C) for age determination.[edit] Furthering the technique and applications
Hessel de Vries, at the University of Groningen furthered the detection methods and applications to a variety of sciences. He has been called "the unsung hero of radiocarbon dating" (cf Willis).


[edit] Basic chemistry
Carbon has two stable, nonradioactive isotopes: carbon-12 (12C), and carbon-13 (13C). In addition, there are tiny amounts of the unstable isotope carbon-14 (14C) on Earth. Carbon-14 has a half-life of 5730 years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth's atmosphere, which forms more of the isotope. (In fact the same process occurs in the nitrogen-rich atmosphere of Saturn's moon Titan.) When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons. The resulting neutrons participate in the following reaction on one of the N atoms being knocked out of a nitrogen (N2) molecule in the atmosphere:

1n + 14N → 14C + 1p

Atmospheric 14C, New Zealand[1] and Austria[2]. The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere. Atmospheric nuclear weapon tests almost doubled the concentration of 14C in the Northern Hemisphere [3].The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km (30,000 to 50,000 ft), and at high geomagnetic latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide. Carbon dioxide also permeates the oceans, dissolving in the water. For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon-14 could be assumed to be continuously produced at a constant rate and therefore that the proportion of radioactive to non-radioactive carbon throughout the Earth's atmosphere and surface oceans is constant: ca. 1 part per trillion (600 billion atoms/mole). For more accurate work, the temporal variations of the atmospheric radiocarbon are compensated for by means of calibration curves. When these curves are used, their accuracy and shape are the factors that determine the accuracy and age obtained for a given sample.

Plants take up atmospheric carbon dioxide by photosynthesis, and are eaten by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives. Once it dies, however, this exchange stops, and the amount of carbon-14 gradually decreases through radioactive decay.

14C → 14N + 0β
By emitting a β particle (beta decay), carbon-14 is changed into stable (non-radioactive) nitrogen-14. This decay can be used to get a measure of how long ago a piece of once-living material died. However, aquatic plants obtain some of their carbon from dissolved carbonates which are likely to be very old, and thus deficient in the carbon-14 isotope, so the method is less reliable for such materials as well as for samples derived from animals with such plants in their food chain.


[edit] Measurements and scales
Measurements are traditionally made by counting the radioactive decay of individual carbon atoms by gas proportional counting or by liquid scintillation counting, but these are relatively insensitive and subject to relatively large statistical uncertainties for small samples (below about 1g carbon). If there is little carbon-14 to begin with, a half-life that long means that very few of the atoms will decay while their detection is attempted (4 atoms/s) /mol just after death, hence e.g. 1 (atom/s)/mol after 10,000 years). Sensitivity has since been greatly increased by the use of accelerator-based mass-spectrometric (AMS) techniques, where all the 14C atoms can be counted directly, rather than only those decaying during the counting interval allotted for each analysis. The AMS technique allows one to date samples containing only a few milligrams of carbon.

Raw radiocarbon ages (i.e., those not calibrated) are usually reported in years "before present" (BP). This is the number of radiocarbon years before 1950, based on a nominal (and assumed constant - see "calibration" below) level of carbon-14 in the atmosphere equal to the 1950 level. They are also based on a slightly off historic value for the half-life maintained for consistency with older publications (see "Radiocarbon half-life" below). See the Note below for the basis of the computations. Corrections for isotopic fractionation have not been included in the present note.

Radiocarbon labs generally report an uncertainty, e.g., 3000±30BP indicates a standard deviation of 30 radiocarbon years. Traditionally this includes only the statistical counting uncertainty and some labs supply an "error multiplier" that can be multiplied by the uncertainty to account for other sources of error in the measuring process. Additional error is likely to arise from the nature and collection of the sample itself, e.g., a tree may accumulate carbon over a significant period of time. Such old wood, turned into an artifact some time after the death of the tree, will reflect the date of the carbon in the wood.

The current maximum radiocarbon age limit lies in the range between 58,000 and 62,000 years. This limit is encountered when the radioactivity of the residual 14C in a sample is too low to be distinguished from the background radiation.


[edit] Calibration

[edit] The need for calibration

Calibration curve for the radiocarbon dating scale. Data sources: Stuiver et al.[4]. Samples with a real date more recent than AD 1950 are dated and/or tracked using the N- & S-Hemisphere graphs. See preceding figure.A raw BP date cannot be used directly as a calendar date, because the level of atmospheric 14C has not been strictly constant during the span of time that can be radiocarbon dated. The level is affected by variations in the cosmic ray intensity which is affected by variations caused by solar storms. In addition there are substantial reservoirs of carbon in organic matter, the ocean, ocean sediments (see methane hydrate), and sedimentary rocks. Changing climate can sometimes disrupt the carbon flow between these reservoirs and the atmosphere. The level has also been affected by human activities—it was almost doubled for a short period due to atomic bomb tests in the 1950s and 1960s and has been reduced by the release of large amounts of CO2 from ancient organic sources where 14C is not present—the fossil fuels used in industry and transportation, known as the Suess effect.


[edit] Calibration methods
The raw radiocarbon dates, in BP years, are therefore calibrated to give calendar dates. Standard calibration curves are available, based on comparison of radiocarbon dates of samples that can be independently dated by other methods such as examination of tree growth rings (dendrochronology), ice cores, deep ocean sediment cores, lake sediment varves, coral samples, and speleothems (cave deposits).

The calibration curves can vary significantly from a straight line, so comparison of uncalibrated radiocarbon dates (e.g., plotting them on a graph or subtracting dates to give elapsed time) is likely to give misleading results. There are also significant plateaus in the curves, such as the one from 11,000 to 10,000 radiocarbon years BP, which is believed to be associated with changing ocean circulation during the Younger Dryas period. The accuracy of radiocarbon dating is lower for samples originating from such plateau periods. It has been noted that the plateau itself can be used as a time marker when it appears in a time series.


[edit] Radiocarbon half-life

[edit] Libby vs Cambridge values
Carbon dating was developed by a team led by Willard Libby. Originally a carbon-14 half-life of 5568±30 years was used, which is now known as the Libby half-life. Later a more accurate figure of 5730±40 years was determined, which is known as the Cambridge half-life. However laboratories continue to use the Libby figure to avoid inconsistencies when comparing raw dates and when using calibration curves to obtain calendrical dates.


[edit] Examples
Haraldskær Woman
Thera eruption
Vinland map
Skeleton Lake
Kennewick Man
Shroud of Turin