Radiocarbon dating can easily establish that humans have been on the earth for over twenty thousand years, at least twice as long as creationists are willing to allow. Therefore it should come as no surprise that creationists at the Institute for Creation Research ICR have been trying desperately to discredit this method for years. They have their work cut out for them, however, because radiocarbon C dating is one of the most reliable of all the radiometric dating methods.
This article will answer several of the most common creationist attacks on carbon dating, using the question-answer format that has proved so useful to lecturers and debaters. Answer: Cosmic rays in the upper atmosphere are constantly converting the isotope nitrogen N into carbon C or radiocarbon. Living organisms are constantly incorporating this C into their bodies along with other carbon isotopes. When the organisms die, they stop incorporating new C, and the old C starts to decay back into N by emitting beta particles.
The older an organism's remains are, the less beta radiation it emits because its C is steadily dwindling at a predictable rate. So, if we measure the rate of beta decay in an organic sample, we can calculate how old the sample is. C decays with a half-life of 5, years. Question: Kieth and Anderson radiocarbon-dated the shell of a living freshwater mussel and obtained an age of over two thousand years.
ICR creationists claim that this discredits C dating. How do you reply? Answer: It does discredit the C dating of freshwater mussels, but that's about all. Kieth and Anderson show considerable evidence that the mussels acquired much of their carbon from the limestone of the waters they lived in and from some very old humus as well. Carbon from these sources is very low in C because these sources are so old and have not been mixed with fresh carbon from.
Thus, a freshly killed mussel has far less C than a freshly killed something else, which is why the C dating method makes freshwater mussels seem older than they really are. When dating wood there is no such problem because wood gets its carbon straight from the air, complete with a full dose of C The creationists who quote Kieth and Anderson never tell you this, however. Question: A sample that is more than fifty thousand years old shouldn't have any measurable C Coal, oil, and natural gas are supposed to be millions of years old; yet creationists say that some of them contain measurable amounts of C, enough to give them C ages in the tens of thousands of years.
How do you explain this? Answer: Very simply. Radiocarbon dating doesn't work well on objects much older than twenty thousand years, because such objects have so little C left that their beta radiation is swamped out by the background radiation of cosmic rays and potassium K decay. Younger objects can easily be dated, because they still emit plenty of beta radiation, enough to be measured after the background radiation has been subtracted out of the total beta radiation.
However, in either case, the background beta radiation has to be compensated for, and, in the older objects, the amount of C they have left is less than the margin of error in measuring background radiation. As Hurley points out:.
Without rather special developmental work, it is not generally practicable to measure ages in excess of about twenty thousand years, because the radioactivity of the carbon becomes so slight that it is difficult to get an accurate measurement above background radiation. Cosmic rays form beta radiation all the time; this is the radiation that turns N to C in the first place.
K decay also forms plenty of beta radiation. Stearns, Carroll, and Clark point out that ". This radiation cannot be totally eliminated from the laboratory, so one could probably get a "radiocarbon" date of fifty thousand years from a pure carbon-free piece of tin. However, you now know why this fact doesn't at all invalidate radiocarbon dates of objects younger than twenty thousand years and is certainly no evidence for the notion that coals and oils might be no older than fifty thousand years.
Question: Creationists such as Cook claim that cosmic radiation is now forming C in the atmosphere about one and one-third times faster than it is decaying. If we extrapolate backwards in time with the proper equations, we find that the earlier the historical period, the less C the atmosphere had.
If we extrapolate. If they are right, this means all C ages greater than two or three thousand years need to be lowered drastically and that the earth can be no older than ten thousand years. Answer: Yes, Cook is right that C is forming today faster than it's decaying. However, the amount of C has not been rising steadily as Cook maintains; instead, it has fluctuated up and down over the past ten thousand years.
How do we know this? From radiocarbon dates taken from bristlecone pines. There are two ways of dating wood from bristlecone pines: one can count rings or one can radiocarbon-date the wood. Since the tree ring counts have reliably dated some specimens of wood all the way back to BC, one can check out the C dates against the tree-ring-count dates. Admittedly, this old wood comes from trees that have been dead for hundreds of years, but you don't have to have an 8,year-old bristlecone pine tree alive today to validly determine that sort of date.
It is easy to correlate the inner rings of a younger living tree with the outer rings of an older dead tree. The correlation is possible because, in the Southwest region of the United States, the widths of tree rings vary from year to year with the rainfall, and trees all over the Southwest have the same pattern of variations.
When experts compare the tree-ring dates with the C dates, they find that radiocarbon ages before BC are really too young—not too old as Cook maintains. For example, pieces of wood that date at about BC by tree-ring counts date at only BC by regular C dating and BC by Cook's creationist revision of C dating as we see in the article, "Dating, Relative and Absolute," in the Encyclopaedia Britannica.
So, despite creationist claims, C before three thousand years ago was decaying faster than it was being formed and C dating errs on the side of making objects from before BC look too young , not too old. Question: But don't trees sometimes produce more than one growth ring per year? Wouldn't that spoil the tree-ring count? Answer: If anything, the tree-ring sequence suffers far more from missing rings than from double rings. This means that the tree-ring dates would be slightly too young, not too old.
Of course, some species of tree tend to produce two or more growth rings per year. But other species produce scarcely any extra rings. Most of the tree-ring sequence is based on the bristlecone pine. This tree rarely produces even a trace of an extra ring; on the contrary, a typical bristlecone pine has up to 5 percent of its rings missing. Concerning the sequence of rings derived from the bristlecone pine, Ferguson says:. In certain species of conifers, especially those at lower elevations or in southern latitudes, one season's growth increment may be composed of two or more flushes of growth, each of which may strongly resemble an annual ring.
In the growth-ring analyses of approximately one thousand trees in the White Mountains, we have, in fact, found no more than three or four occurrences of even incipient multiple growth layers. In years of severe drought, a bristlecone pine may fail to grow a complete ring all the way around its perimeter; we may find the ring if we bore into the tree from one angle, but not from another.
Hence at least some of the missing rings can be found. Even so, the missing rings are a far more serious problem than any double rings. Other species of trees corroborate the work that Ferguson did with bristlecone pines. Before his work, the tree-ring sequence of the sequoias had been worked out back to BC. The archaeological ring sequence had been worked out back to 59 BC. The limber pine sequence had been worked out back to 25 BC. The radiocarbon dates and tree-ring dates of these other trees agree with those Ferguson got from the bristlecone pine.
But even if he had had no other trees with which to work except the bristlecone pines, that evidence alone would have allowed him to determine the tree-ring chronology back to BC. See Renfrew for more details. So, creationists who complain about double rings in their attempts to disprove C dating are actually grasping at straws. If the Flood of Noah occurred around BC, as some creationists claim, then all the bristlecone pines would have to be less than five thousand years old.
This would mean that eighty-two hundred years worth of tree rings had to form in five thousand years, which would mean that one-third of all the bristlecone pine rings would have to be extra rings. Creationists are forced into accepting such outlandish conclusions as these in order to jam the facts of nature into the time frame upon which their "scientific" creation model is based.
Question: Creationist Thomas G. Barnes has claimed that the earth's magnetic field is decaying exponentially with a half-life of fourteen hundred years. Not only does he consider this proof that the earth can be no older than ten thousand years but he also points out that a greater magnetic strength in the past would reduce C dates.
Now if the magnetic field several thousand years ago was indeed many times stronger than it is today, there would have been less cosmic radiation entering the atmosphere back then and less C would have been produced. Therefore, any C dates taken from objects of that time period would be too high. How do you answer him? Answer: Like Cook, Barnes looks at only part of the evidence. What he ignores is the great body of archaeological and geological data showing that the strength of the magnetic field has been fluctuating up and down for thousands of years and that it has reversed polarity many times in the geological past.
So, when Barnes extrapolates ten thousand years into the past, he concludes that the magnetic field was nineteen times stronger in BC than it is today, when, actually, it was only half as intense then as now. This means that radiocarbon ages of objects from that time period will be too young, just as we saw from the bristlecone pine evidence. Question: But how does one know that the magnetic field has fluctuated and reversed polarity? Aren't these just excuses scientists give in order to neutralize Barnes's claims?
Answer: The evidence for fluctuations and reversals of the magnetic field is quite solid. Bucha, a Czech geophysicist, has used archaeological artifacts made of baked clay to determine the strength of the earth's magnetic field when they were manufactured.
He found that the earth's magnetic field was 1. See Bailey, Renfrew, and Encyclopedia Britannica for details. And yet these studies Materials provided by Cornell University. Original written by Daniel Aloi. Note: Content may be edited for style and length. Science News. The Cornell-led team questioned those assumptions. Story Source: Materials provided by Cornell University. Journal Reference : Sturt W. Timothy Jull, Todd E. Fluctuating radiocarbon offsets observed in the southern Levant and implications for archaeological chronology debates.
ScienceDaily, 5 June Cornell University. Inaccuracies in radiocarbon dating. Retrieved April 11, from www. Using a recently developed method, based on the presence of sudden spikes in carbon ScienceDaily shares links with sites in the TrendMD network and earns revenue from third-party advertisers, where indicated.
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 December In nature, carbon exists as two stable, nonradioactive isotopes : carbon 12 C , and carbon 13 C , and a radioactive isotope, carbon 14 C , also known as "radiocarbon". 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 decrease 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 ,  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.
Because 14 C decays at a known rate, the proportion of radiocarbon can be used to determine how long it has been since a given sample stopped exchanging carbon — the older the sample, the less 14 C will be left. 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. 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,  and each component is also referred to individually as a carbon exchange reservoir.
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 :    comparison of overlapping series of tree rings allowed the construction of a continuous sequence of tree-ring data that spanned 8, years.
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 into the atmosphere, resulting in the creation of 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.
The carbon exchange between atmospheric CO 2 and carbonate at the ocean surface is also subject to fractionation, with 14 C in the atmosphere more likely than 12 C to dissolve in the ocean. This increase in 14 C concentration almost exactly cancels out the decrease caused by the upwelling of water containing old, and hence 14 C depleted, carbon from the deep ocean, so that direct measurements of 14 C radiation are similar to measurements for the rest of the biosphere.
Correcting for isotopic fractionation, as is done for all radiocarbon dates to allow comparison between results from different parts of the biosphere, gives an apparent age of about years for ocean surface water.
The marine effect : The CO 2 in the atmosphere transfers to the ocean by dissolving in the surface water as carbonate and bicarbonate ions; at the same time the carbonate ions in the water are returning to the air as CO 2. The deepest parts of the ocean mix very slowly with the surface waters, and the mixing is uneven. The main mechanism that brings deep water to the surface is upwelling, which is more common in regions closer to the equator.
Upwelling is also influenced by factors such as the topography of the local ocean bottom and coastlines, the climate, and wind patterns. Overall, the mixing of deep and surface waters takes far longer than the mixing of atmospheric CO 2 with the surface waters, and as a result water from some deep ocean areas has an apparent radiocarbon age of several thousand years.
Upwelling mixes this "old" water with the surface water, giving the surface water an apparent age of about several hundred years after correcting for fractionation. The northern and southern hemispheres have atmospheric circulation systems that are sufficiently independent of each other that there is a noticeable time lag in mixing between the two.
Since the surface ocean is depleted in 14 C because of the marine effect, 14 C is removed from the southern atmosphere more quickly than in the north. For example, rivers that pass over limestone , which is mostly composed of calcium carbonate , will acquire carbonate ions.
Similarly, groundwater can contain carbon derived from the rocks through which it has passed. Volcanic eruptions eject large amounts of carbon into the air. Dormant volcanoes can also emit aged carbon. Any addition of carbon to a sample of a different age will cause the measured date to be inaccurate. Contamination with modern carbon causes a sample to appear to be younger than it really is: the effect is greater for older samples.
Samples for dating need to be converted into a form suitable for measuring the 14 C content; this can mean conversion to gaseous, liquid, or solid form, depending on the measurement technique to be used. Before this can be done, the sample must be treated to remove any contamination and any unwanted constituents.
Particularly for older samples, it may be useful to enrich the amount of 14 C in the sample before testing. This can be done with a thermal diffusion column. Once contamination has been removed, samples must be converted to a form suitable for the measuring technology to be used.
For accelerator mass spectrometry , solid graphite targets are the most common, although gaseous CO 2 can also be used. The quantity of material needed for testing depends on the sample type and the technology being used. There are two types of testing technology: detectors that record radioactivity, known as beta counters, and accelerator mass spectrometers.
For beta counters, a sample weighing at least 10 grams 0. For decades after Libby performed the first radiocarbon dating experiments, the only way to measure the 14 C in a sample was to detect the radioactive decay of individual carbon atoms. Libby's first detector was a Geiger counter of his own design. He converted the carbon in his sample to lamp black soot and coated the inner surface of a cylinder with it.
This cylinder was inserted into the counter in such a way that the counting wire was inside the sample cylinder, in order that there should be no material between the sample and the wire. Libby's method was soon superseded by gas proportional counters , which were less affected by bomb carbon the additional 14 C created by nuclear weapons testing. These counters record bursts of ionization caused by the beta particles emitted by the decaying 14 C atoms; the bursts are proportional to the energy of the particle, so other sources of ionization, such as background radiation, can be identified and ignored.
The counters are surrounded by lead or steel shielding, to eliminate background radiation and to reduce the incidence of cosmic rays. In addition, anticoincidence detectors are used; these record events outside the counter and any event recorded simultaneously both inside and outside the counter is regarded as an extraneous event and ignored.
The other common technology used for measuring 14 C activity is liquid scintillation counting, which was invented in , but which had to wait until the early s, when efficient methods of benzene synthesis were developed, to become competitive with gas counting; after liquid counters became the more common technology choice for newly constructed dating laboratories.
The counters work by detecting flashes of light caused by the beta particles emitted by 14 C as they interact with a fluorescing agent added to the benzene. Like gas counters, liquid scintillation counters require shielding and anticoincidence counters. For both the gas proportional counter and liquid scintillation counter, what is measured is the number of beta particles detected in a given time period.
Each measuring device is also used to measure the activity of a blank sample — a sample prepared from carbon old enough to have no activity. This provides a value for the background radiation, which must be subtracted from the measured activity of the sample being dated to get the activity attributable solely to that sample's 14 C.
In addition, a sample with a standard activity is measured, to provide a baseline for comparison. The ions are accelerated and passed through a stripper, which removes several electrons so that the ions emerge with a positive charge. A particle detector then records the number of ions detected in the 14 C stream, but since the volume of 12 C and 13 C , needed for calibration is too great for individual ion detection, counts are determined by measuring the electric current created in a Faraday cup.
Any 14 C signal from the machine background blank is likely to be caused either by beams of ions that have not followed the expected path inside the detector or by carbon hydrides such as 12 CH 2 or 13 CH. A 14 C signal from the process blank measures the amount of contamination introduced during the preparation of the sample.
These measurements are used in the subsequent calculation of the age of the sample. The calculations to be performed on the measurements taken depend on the technology used, since beta counters measure the sample's radioactivity whereas AMS determines the ratio of the three different carbon isotopes in the sample.
To determine the age of a sample whose activity has been measured by beta counting, the ratio of its activity to the activity of the standard must be found. To determine this, a blank sample of old, or dead, carbon is measured, and a sample of known activity is measured. The additional samples allow errors such as background radiation and systematic errors in the laboratory setup to be detected and corrected for. The results from AMS testing are in the form of ratios of 12 C , 13 C , and 14 C , which are used to calculate Fm, the "fraction modern".
Both beta counting and AMS results have to be corrected for fractionation. The calculation uses 8,, the mean-life derived from Libby's half-life of 5, years, not 8,, the mean-life derived from the more accurate modern value of 5, years. Libby's value for the half-life is used to maintain consistency with early radiocarbon testing results; calibration curves include a correction for this, so the accuracy of final reported calendar ages is assured. The reliability of the results can be improved by lengthening the testing time.
Radiocarbon dating is generally limited to dating samples no more than 50, years old, as samples older than that have insufficient 14 C to be measurable. Older dates have been obtained by using special sample preparation techniques, large samples, and very long measurement times.
These techniques can allow measurement of dates up to 60, and in some cases up to 75, years before the present. This was demonstrated in by an experiment run by the British Museum radiocarbon laboratory, in which weekly measurements were taken on the same sample for six months.
The measurements included one with a range from about to about years ago, and another with a range from about to about Errors in procedure can also lead to errors in the results. The calculations given above produce dates in radiocarbon years: i. To produce a curve that can be used to relate calendar years to radiocarbon years, a sequence of securely dated samples is needed which can be tested to determine their radiocarbon age.
The study of tree rings led to the first such sequence: individual pieces of wood show characteristic sequences of rings that vary in thickness because of environmental factors such as the amount of rainfall in a given year. These factors affect all trees in an area, so examining tree-ring sequences from old wood allows the identification of overlapping sequences.
In this way, an uninterrupted sequence of tree rings can be extended far into the past. The first such published sequence, based on bristlecone pine tree rings, was created by Wesley Ferguson. Suess said he drew the line showing the wiggles by "cosmic schwung ", by which he meant that the variations were caused by extraterrestrial forces. It was unclear for some time whether the wiggles were real or not, but they are now well-established.
A calibration curve is used by taking the radiocarbon date reported by a laboratory and reading across from that date on the vertical axis of the graph. The point where this horizontal line intersects the curve will give the calendar age of the sample on the horizontal axis. This is the reverse of the way the curve is constructed: a point on the graph is derived from a sample of known age, such as a tree ring; when it is tested, the resulting radiocarbon age gives a data point for the graph.
Over the next thirty years many calibration curves were published using a variety of methods and statistical approaches. The IntCal20 data includes separate curves for the northern and southern hemispheres, as they differ systematically because of the hemisphere effect. The southern curve SHCAL20 is based on independent data where possible and derived from the northern curve by adding the average offset for the southern hemisphere where no direct data was available.
The sequence can be compared to the calibration curve and the best match to the sequence established. This "wiggle-matching" technique can lead to more precise dating than is possible with individual radiocarbon dates. Bayesian statistical techniques can be applied when there are several radiocarbon dates to be calibrated. For example, if a series of radiocarbon dates is taken from different levels in a stratigraphic sequence, Bayesian analysis can be used to evaluate dates which are outliers and can calculate improved probability distributions, based on the prior information that the sequence should be ordered in time.
Several formats for citing radiocarbon results have been used since the first samples were dated. As of , the standard format required by the journal Radiocarbon is as follows. Related forms are sometimes used: for example, "10 ka BP" means 10, radiocarbon years before present i.
The curve used to calibrate the results should be the latest available IntCal curve. Calibrated dates should also identify any programs, such as OxCal, used to perform the calibration. A key concept in interpreting radiocarbon dates is archaeological association : what is the true relationship between two or more objects at an archaeological site?
It frequently happens that a sample for radiocarbon dating can be taken directly from the object of interest, but there are also many cases where this is not possible. Metal grave goods, for example, cannot be radiocarbon dated, but they may be found in a grave with a coffin, charcoal, or other material which can be assumed to have been deposited at the same time.
In these cases, a date for the coffin or charcoal is indicative of the date of deposition of the grave goods, because of the direct functional relationship between the two. There are also cases where there is no functional relationship, but the association is reasonably strong: for example, a layer of charcoal in a rubbish pit provides a date which has a relationship to the rubbish pit.
Contamination is of particular concern when dating very old material obtained from archaeological excavations and great care is needed in the specimen selection and preparation. In , Thomas Higham and co-workers suggested that many of the dates published for Neanderthal artefacts are too recent because of contamination by "young carbon".
Although the recalibration mostly results in subtle changes, even tiny tweaks can make a huge difference for archaeologists and paleo-ecologists aiming to pin events to a small window of time. The basis of radiocarbon dating is simple: all living things absorb carbon from the atmosphere and food sources around them, including a certain amount of natural, radioactive carbon Measuring the amount left over gives an estimate as to how long something has been dead. In recent decades, the burning of fossil fuel and tests of nuclear bombs have radically altered the amount of carbon in the air, and there are non-anthropogenic wobbles going much further back.
During planetary magnetic-field reversals, for example, more solar radiation enters the atmosphere, producing more carbon The oceans also suck up carbon — a little more so in the Southern Hemisphere, where there is more ocean — and circulate it for centuries, further complicating things. As a result, conversion tables are needed that match up calendar dates with radiocarbon dates in different regions. They will be published in the journal Radiocarbon in the next few months. Since the s, researchers have mainly done this recalibration with trees, counting annual rings to get calendar dates and matching those with measured radiocarbon dates.
The oldest single tree for which this has been done, a bristlecone pine from California, was about 5, years old. By matching up the relative widths of rings from one tree to another, including from bogs and historic buildings, the tree record has now been pushed back to 13, years ago. World's largest hoard of carbon dates goes global.
In , some stalagmites in Hulu Cave in China provided a datable record stretching back 54, years 1. Higham says the recalibration is fundamental for understanding the chronology of hominins living 40, years ago. IntCal20 revises the date for a Homo sapiens jawbone found in Romania called Oase 1, potentially making it hundreds of years older than previously thought 2. Genetic analyses of Oase 1 have revealed that it had a Neanderthal ancestor just four to six generations back, says Higham, so the older the Oase 1 date, the further back Neanderthals were living in Europe.
Meanwhile, the oldest H. Divided by DNA: The uneasy relationship between archaeology and ancient genomics. Others will use the recalibration to assess environmental events. For example, researchers have been arguing for decades over the timing of the Minoan eruption at the Greek island of Santorini.
Until now, radiocarbon results typically gave a best date in the low s BC, about years older than given by most archaeological assessments. IntCal20 improves the accuracy of dating but makes the debate more complicated: overall, it bumps the calendar dates for the radiocarbon result about 5—15 years younger, but — because the calibration curve wiggles around a lot — it also provides six potential time windows for the eruption, most likely in the low s BC, but maybe in the high s BC 2.
So the two groups still disagree, says Reimer, but less so, and with more complications. Cheng, H. Science , — Download references. Article 31 MAR Research Highlight 30 MAR An essential round-up of science news, opinion and analysis, delivered to your inbox every weekday.
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