Is the Wood Recently Found on Mt. Ararat from the Ark?

On April 25, 2010, a press conference was held in Hong Kong to announce to the world the potential discovery of the remains of Noah’s Ark on Mt. Ararat in Turkey by a joint Chinese–Turkish team of explorers. Both before and after this press conference, representatives of the discovery team had cautiously been seeking to make contact with sympathetic scientists whose positive support they hoped to enlist.

A Skype Conference Call

Consequently, on April 20, 2010, I participated in a Skype conference call (early morning in northern Kentucky, USA) with several Chinese members of the discovery team (late evening for them in Hong Kong). During that conference call I was shown video footage of the team’s exploration on Mt. Ararat, footage that was subsequently released at the press conference. Photos of a wooden structure purportedly buried on Mt. Ararat, and of the inside of it, were also provided (for example, Figure 1).

Figure 1. One of the photos released by the discovery team of the inside of the wooden structure claimed to be part of the remains of the Ark which they found on Mt. Ararat. (View larger image)

As a scientist I am always cautious and somewhat skeptical of bold and spectacular claims, especially when made in defense of the Bible, yet as a Bible-believing Christian the thought of this wooden structure being the remains of the Ark was tantalizing. Friends in Hong Kong who helped arrange this confidential conference call were equally cautious but excited. We were all looking for the unequivocal evidence that would convince us that this was indeed the remains of the long-sought-after Ark. Such a discovery would be another powerful witness to the truth and authority of God’s Word.1

These Chinese members of the discovery team wanted to determine if I would be sympathetic to their claims, and able to participate with them in their planned press conference, to appear as an “expert witness” to corroborate their potential discovery. I would have seriously considered their request if they could convince me that this discovery was genuine. I was already skeptical though, because the Bible tells us the Ark landed on “the mountains of Ararat” halfway through the Flood on day 150 (Genesis 8:4), rather than on Mt. Ararat itself, which is mostly a recent volcano that has erupted numerous times in recent history.

Even so, during our conference call I asked whether any scientific tests had already been conducted. It was quickly indicated that samples of wood from the structures on Mt. Ararat had been tested for radiocarbon (C-14). My curiosity was naturally aroused, as such tests would potentially be a good indication of the structure’s possible antiquity. So without any hesitation on their part, these Chinese members of the discovery team tabled their full compilation of C-14 test results, and sent me a copy.

What I saw immediately convinced me, that if these C-14 test results were obtained on wood samples from the structure they had discovered on Mt. Ararat, then they had definitely NOT discovered the Ark. I graciously sought to explain this to our conference call hosts, giving the reasons for my coming to that conclusion. I also strongly urged them to have further C-14 testing done on their wood samples, and other scientific tests performed on samples of a rope and white pellets we’d seen in the video footage and photos. I even suggested that they delay their press conference until such time as extra scientific tests had been done.

That conference call ended amicably. It wasn’t clear whether our Chinese hosts had understood my explanations as to how and why their C-14 tests proved their wood samples are NOT from the remains of the Ark. They had asked that the C-14 test results remained confidential.

The Press Conference and Its Aftermath

The discovery team went ahead with their planned press conference in Hong Kong on April 25, 2010, and announced to the world’s media that the Ark had been discovered on Mt. Ararat. At the press conference, wood, rope and white pellet samples were on display (Figure 2). The five-page press release was entitled: “Exploration team successfully ventures inside 4,800-year-old wooden structure on snow-capped Mt. Ararat. Experts and Turkish officials believe artefact is Noah’s Ark.” Yet all that appeared in the press release concerning the dating of the wood was: “Wood specimens were dated as 4,800 years old.” That simple statement was understood to mean that more than one sample was dated at 4,800 years old, but no mention was made of what dating method was used.

Figure 2. The samples of white pellets, rope and wood on display at the press conference in Hong Kong on April 25, 2010, which the discovery team claimed came from the wooden remains on Mt. Ararat purported to be the Ark. (View larger image)

In response to the ensuing media blitz, AiG posted on its website a brief report on April 27, 2010, and brief comments on April 29, 2010, followed by a lengthier news item on May 1, 2010, in the weekly News to Note feature. Only in the latter news item was the radiocarbon dating of the wood samples briefly mentioned, with incomplete details (I was incommunicado in the Grand Canyon at the time!). But the AiG news item did briefly explain why the radiocarbon dates obtained from the discovery team’s wood samples were problematic, if indeed this was pre-Flood wood from the Ark.

Rather than engage in a public discussion over the C-14 dating of the wood samples, efforts continued to be made behind the scenes to convince the discovery team to fully disclose the C-14 test results they had obtained, and to undertake further C-14 testing of their wood samples, plus scientific testing of the samples of rope and white pellets. Those efforts seem to have failed, as to my knowledge the full details of the C-14 testing of their wood samples have never been publicly disclosed by the discovery team. Nor am I aware that any scientific testing of the samples of rope and white pellets has been done and publicly reported.

Meanwhile, a dramatic, full-length feature film has been produced by the discovery team, publicizing their claim to have found the Ark on Mt. Ararat, proclaiming that the biblical record is therefore true, and sharing the Gospel on that basis. The film is also being used to raise funds for further exploration and documentary production, with the same evangelistic purposes. The premiere screening was in Sydney, Australia, with the film being subsequently shown in other Australian capital cities, including recently in Brisbane. Other film showings have occurred in Hong Kong and Taiwan, and now the film is being released in the USA.

Several U.S. Christian academics are shown in the film, portrayed as lending their support to the claim that the Ark has been discovered on Mt. Ararat. As a result, many Christians have been enthralled if not convinced by this purportedly incredible archaeological discovery. Consequently, many have donated funds towards the cost of further Ararat expeditions in the hope that other documentary films will be forthcoming to be used for evangelistic purposes.

The Undisclosed C-14 Test Results

However, the full details of the C-14 testing of the wood samples from this wooden structure on Mt. Ararat that is claimed in this film to be the Ark have still not been disclosed to film audiences. Neither do these results seem to have been disclosed to some of the U.S. Christian academics who feature in the film. If the results have been disclosed to these advisors, the implications do not seem to have been fully understood by those advisors. This is a very serious concern. These academic consultants and the film audiences are not aware that this crucial C-14 evidence actually undermines the Ark discovery claim.

The Chinese–Turkish discovery team claims that they secured wood samples from wooden structures high on Mt. Ararat. While this certainly is attention worthy, what many find troubling is their assertion that subsequent C-14 testing of those wood samples buttresses their claim that those fragments are in fact part of the Ark. Furthermore, the discovery team has chosen not to make their C-14 test results publicly available for scientific scrutiny. Therefore, since people are being seriously misled, and are generously donating under apparently false pretenses, I have prayerfully concluded that I have a Christian responsibility and intellectual obligation to provide these U.S. Christian academics and the Christian public with the full details and implications of the C-14 testing undertaken by the Chinese–Turkish discovery team.

A compilation of the C-14 test results for their wood samples is provided in Table 1, exactly as it was given to me on April 20, 2010 by the Chinese members of the discovery team, in the file they sent me. To ensure the reader will not miss their data, I have taken the liberty to clean up the layout to enhance clarity, readability, and comprehension. The results themselves have not been altered in any way.

It should be clear immediately from the table that four wood samples were C-14 tested, and three laboratories were used. We were not told the identity of these laboratories, so I have no way of assessing the quality of these C-14 analyses. Presumably, they are reputable laboratories, but no indications were given as to which analytical equipment was used to do the testing, whether by the older beta counting method, or by the newer (more sophisticated and accurate) accelerator mass spectrometry (AMS) method.

C-14 Dates of Samples A, B, and C

Sample A was analyzed by both Laboratory 1 and Laboratory 2, and both laboratories obtained essentially the same result. This wood sample came from a tree growing since 1955, because the wood had a C-14 activity level greater than the modern level, indicating contamination with C-14 generated by nuclear weapons testing in the atmosphere.2 So obviously this wood sample A could NOT have come from any wooden structure that is the remains of the Ark, even if this wood was found on Mt. Ararat.

Sample B was also analysed by both Laboratory 1 and Laboratory 2, and again both laboratories obtained essentially the same results. This wood sample is dated at 120±25 years BP and 135±30 years BP. Thus this wood sample possibly came from a tree living between 95 and 165 years prior to AD 1950, the zero reference point or datum for BP (Before Present).3 That is, the tree was possibly living sometime between AD 1785 and AD 1855. Thus wood sample B also could NOT have come from any wooden structure that is the remains of the Ark.

In the Remarks column of Table 1 there is a note that Samples A and B “were practically collected from the same site.” A query was also made about “whether the samples were contaminated by moss and bacteria growth”. The laboratory evidently replied that “the older age of sample B might be due to Suess Effect of diluted C-14 by fossil fuel.”

What this comment regarding the Suess Effect is referring to is the observation that, as a result of the Industrial Revolution there was so much burning of fossil fuels, particularly coal, the carbon dioxide produced by that burning diluted the C-14 in the atmosphere.4 Consequently, trees growing in the 1800s photosynthesized less C-14 than trees photosynthesize today, so the wood from the 1800s trees should give ages slightly older than their true ages.

Sample C was only analysed by Laboratory 1, and yielded a C-14 date of 610±25 years BP. Thus this wood sample would appear to be from a tree living sometime between 585 and 635 years prior to AD 1950, that is, between AD 1315 and AD 1365. Once again, this third wood sample also could NOT have come from any wooden structure that is the remains of the Ark. Thus three of the four wood samples categorically do NOT support the claim the Chinese-Turkish exploration team has found the wooden remains of the Ark on Mt. Ararat.

Interestingly, it was reported to Laboratory 1 that samples B and C belonged to the same wooden structure, so that laboratory was asked to try and explain the apparent great age difference between their two analyses (see Remarks column in Table 1): 120±25 years BP (sample B) and 610±25 years BP (sample C). The laboratory’s response was that, even though they did not know how and where the team collected these samples, they were able to determine that sample “C was from the inner part of the tree and (sample) B was (from) the bark.” If so, then the tree(s) from which these two wood samples may have come would have grown for at least 490 years. Nevertheless, such an interpretation by the laboratory is rather conjectural, at best, by their own admission.

Contamination Can Be Ruled Out

The question of potential contamination is important to discuss here, as there is a lot of misunderstanding and confusion (including, perhaps, among the discovery team and its U.S. academic and scientific advisors) about how it might supposedly affect C-14 dating of samples. Obviously, samples need to be collected in the field with proper care to reduce the risk of contamination. However, such concerns are usually overstated by those who have little or no knowledge of how radiocarbon laboratories handle samples before the C-14 testing is performed. Any contamination due to field handling during collection and laboratory processing of samples can be effectively ruled out, due to the harsh chemical pre-treatment of samples in the laboratory prior to final preparation of the samples for the C-14 analyses.

Most laboratories typically follow a modified AAAOx pre-treatment to guarantee the elimination of any contamination, including that from any moss or bacteria.5 First, the samples are drenched in hot and strong hydrochloric acid to dissolve away any contaminant inorganic minerals, such as calcium, barium or strontium salts. Then the samples are soaked for at least a week in a hot and strong mixture of hydrochloric and hydrofluoric acids. After this, any acid-soluble humics are removed from what remains of the samples with an extended hot and strong hydrochloric acid treatment. Finally, this pre-treatment is followed by an extended cold and fresh alkali extraction.

The δ¹³C Parameter

One other detail in Table 1 needs commenting on here. In the Details column is the notation δ¹³C. This is an extra measurement Laboratory 1 performed on samples A, B and C, and Laboratory 2 performed on sample B. It also indicates that these two laboratories probably used the more sophisticated accelerator mass spectrometer (AMS) equipment to do the C-14 measurements, as the C-13 to C-12 ratio needed to calculate the δ¹³C value is a by-product of C-14 measurements using that equipment.

For a technical discussion of this parameter, see the Appendix below. However, in summary, it can be concluded that the δ¹³C values measured by these two laboratories verify that the samples they were C-14 dating were indeed wood, because the δ¹³C values they measured were within the range for recent and fossil woods.

The Fourth Sample—Sample D

In spite of the young ages obtained for three of the four wood samples, it was only the dating of the fourth wood sample that was the basis of the press release that a 4,800-year-old wooden structure had been discovered on Mt. Ararat. This fourth sample, sample D, was only analysed at one laboratory, and that was Laboratory 3 (Table 1), a different laboratory than the ones where the other three samples were analyses Why the different laboratory? Could it be that the discovery team was dissatisfied with the ages yielded by the first three samples in the first two laboratories which were too young and recent to have come from the Ark, so they chose a new laboratory to date this fourth sample? Or was it simply that this sample was larger than the other samples which could be brought out unnoticed for testing at laboratories outside the country, and so sample D had to be analyses at a laboratory closer to Mt. Ararat, for example, across the nearby border in Iran? It is not too surprising that there are now even area rumors circulating that Laboratory 3, for a price, fabricated the needed C-14 age for sample D. Proper and transparent dating methodology should not leave the academic community speculating with such puzzling questions.

Regardless, sample D yielded a C-14 age of 4,269–4,800 years BP (Table 1). Obviously, the discovery team had seized on this result and only quoted in the press conference and press release the higher number in the date range, namely, 4,800 years. The appeal of the 4,800 year age for this wooden structure on Mt. Ararat is that the traditional date for the Flood is 4,350-4,500 years ago, using a tight chronology calculated from the genealogies in the Masoretic text of the Hebrew Old Testament. Furthermore, the pre-Flood wood used to build the Ark would have grown on trees over several hundred years prior to the Flood year, so the 4,800 year date for this wood sample was exactly what the discovery team wanted and was therefore expecting. Thus the dates for the other three wood samples were ignored or (privately) explained away by the discovery team and/or their advisors, because they inconveniently yielded ages that were too young and recent.

The results reported by Laboratory 3 for wood sample D were not as simple as the announced 4,800 year age.

However, the results reported by Laboratory 3 for wood sample D were not as simple as the announced 4,800 year age. In the Remarks column of Table 1 it is stated that both radiocarbon and dendrochronology were used to date wood sample D. The laboratory thus evidently reported a “calendric age” of 6,891±4,647 years cal BP (calibrated BP), the 68% cal BP range. In other words, they concluded that this wood sample was between 2,243 and 11,538 years BP old. Or to put it another way, they reported the age as 4,941±4,647 years cal BC (calibrated BC), namely, the tree from which this wood came died sometime in the years 294-9,858 BC. All these dates, with their reported very large uncertainties, are very different from the emphatic 4,800 year age announced at the press conference and in the press release.

It is intriguing that, in the Remarks column of Table 1, it is indicated that dendrochronology was also used to date sample D. In that method, otherwise known as tree-ring dating, the widths and patterns of the growth rings found in wood samples are measured and then compared against a master tree-ring chronology.6 Master tree-ring chronologies for different tree varieties have been established by comparing the growth rings in various living long-lived trees with woods from previous forests of these trees used in very old buildings and found in archaeological sites. However, the method of comparing and correlating tree rings between different trees and woods is highly subjective, and matches are often first established using C-14 dating. Thus dendrochronology is not objectively independent of C-14 dating. Furthermore, it assumes only an annually repetitive pattern of tree rings. However, in the early post-Flood there are good scientific reasons to think that world climatic conditions would have varied almost weekly, rather than following an annual repetitive pattern, resulting in multiple growth rings in trees per year. So to examine the few growth rings in a small wood sample of unknown tree origin or variety and to apparently use dendrochronology to date it is highly subjective and speculative at best.

In any case, the announced 4,800 year date for the wood sample D is based on unsound reasoning on the part of the discovery team. All appearances indicate that they are unaware of the numerous C-14 dating results obtained on pre-Flood wood and other fossils, and simply do not understand the problems with the C-14 dating method.

C-14 Dates for Pre-Flood Fossilized Wood

Within the biblical framework of earth history, the Flood was responsible for producing, in about one year, the bulk of the fossil record preserved in the earth’s surface sedimentary rock layers, conventionally dated by secular geologists as being up to 540 or more million years old. Thus the animals and plants that have been preserved as fossils in the rock record were animals and plants that were alive in the latter years of the pre-Flood era just before the Flood catastrophe occurred. Thus wood found fossilized in the geologic record would represent trees that were in forests from which Noah also obtained the wood to build the Ark. Consequently, if we were to find the wooden remains of the Ark, then that wood should yield C-14 test results similar to whatever C-14 is found in fossilized wood, since both represent the remains of pre-Flood trees.

Measurable C-14 has been detected in fossils from the earliest days of radiocarbon dating. In many instances, according to their supposed millions-of-years ages those fossils should be completely C-14-dead. In other words, all the original C-14 initially in them should have decayed away, so they should not have any C-14 left in them. This is because C-14 has a half-life (or decay rate) of 5,730 years. If any organism or plant when it was buried and fossilized contained the level of C-14 currently in plants and animals, then after only one million years, corresponding to 174.5 C-14 half-lives, the fraction of the original C-14 remaining would be 3×10^-53. However, a mass of C-14 equal to the entire mass of the earth contains only about 3×10⁵⁰ C-14 atoms.7 Thus, not a single atom of C-14 formed even one million years ago anywhere in or on the earth should conceivably still exist. Therefore, there should be absolutely no measurable C-14 able to be detected in fossils claimed to be a million or more years old. On the other hand, if the fossils are the remains of animals and plants that lived prior to the Flood and were then destroyed and buried to become fossils during the Flood only 4,500 years ago, all fossils should therefore still have measurable C-14 in them.

A well-kept “secret” and fact is that they do! A survey of all the C-14 dates reported in the journal Radiocarbon up to 1970 found that for more than 15,000 samples, all such fossilized organic matter was “dateable within 50,000 years as published.”8 These samples included coal, oil, natural gas, and other allegedly very ancient (> one million years old) fossil materials. The scientific community never took these anomalies seriously, because these measurements were obtained using the beta-decay counting method, by which it was difficult to distinguish between the decay of C-14 atoms and background cosmic rays. Thus, for samples such as these that were claimed to be so old they should be C-14 dead, the measurable C-14 levels detected were simply dismissed as due to measurement errors.9

The accelerator mass spectrometer (AMS) method was developed in the early 1980s. It counts C-14 atoms directly and is thus not compromised by background cosmic rays, so it is far more accurate. Thus a further tabulation of about 70 superior AMS measurements published between 1984 and 1998 in the standard radiocarbon literature shows that all of the fossilized organic materials analyses yielded significant levels of C-14 when according to their claimed millions-of-years ages they should have been entirely C-14 dead.10 These organic materials included not only fossilized wood, but natural graphite, coal, natural gas, oil, fossilized shells and bones, and even marble, from every portion of the geologic record of the Flood. All contained detectable C-14 levels well above the AMS limits of detection. It was argued that instrument error as an explanation for these results could be eliminated on experimental grounds, and that contamination of the C-14-bearing fossil material in situ was unlikely. Proper laboratory procedures had also eliminated any contamination during field collection and sample preparation. Therefore, it is concluded that the detectable C-14 in these samples most likely originates from the original organisms themselves, including the original pre-Flood trees.

Additional C-14 dating studies of fossilized woods have been undertaken, with samples from various strata levels in the geologic record of the Flood conventionally dated as 30-250 million years old.11 The fossilized wood samples (see Figure 3) were C-14 tested using the AMS method at two laboratories. In all cases the measured C-14 levels were well above the AMS limit of detection (meaning that the AMS measurements were accurate), with the values equating to C-14 ages of between 20,700±1,200 years and 44,700±950 years (see Table 2).

(a) Oligocene wood from the Cresson Mine, Cripple Creek, Colorado, USA.

(b) Eocene wood from the Crinum Mine, central Queensland, Australia.

(c) Jurassic wood from the Horton Quarry, Edge Hill, Warwickshire, England, UK.

(d) Triassic wood from the Hawkesbury Sandstone, Bundanoon, New South Wales, Australia.

Figure 3. Fossil wood from the geologic record of the Flood that was C-14 dated (see Table 2).

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In another study, ten coal samples from the U.S. Department of Energy Coal Sample Bank maintained at Pennsylvania State University were selected as representative of U.S. coal beds geographically, as well as with respect to depth in the geologic record of the Flood.12 Coal is buried and fossilized plant material, including wood. These coal samples were from Eocene, Cretaceous, and Pennsylvanian coal beds spanning 40–300 million years on the conventional geologic timescale. The AMS analyses detected C-14 levels in all ten coal samples equivalent to an age range of between 48,000 and 50,000 years. In other words, irrespective of their claimed 40–300 million years ages, the trees buried in these coal beds all yielded the same C-14 age of 48,000–50,000 years, consistent with them all being buried and fossilized at the same time, which is also consistent with these coal beds all having formed during the Flood year of the biblical timescale only 4,500 years ago.

Why Does Pre-Flood Wood Yield Inflated C-14 Ages?

It is clear then from the C-14 dates obtained on pre-Flood wood buried and fossilized during the Flood, as listed in Table 2, and pre-Flood wood buried and fossilized in coal beds (also deposited during the Flood), that if wood found today on Mt. Ararat were to be pre-Flood wood used to build the Ark, then it should yield a C-14 age of between 20,000 and 50,000 years. The obvious question then is why pre-Flood wood, being only 4,500 years or so old according to the biblical timeframe based on a tight chronology calculated from the genealogies in the Masoretic text of the Hebrew Old Testament, would give such inflated C-14 ages of between 20,000 and 50,000 years?

All these C-14 dates calculated from the AMS C-14 analyses of these fossil woods and coal beds are based on the assumption that the modern atmospheric C-14/total-C ratio existed when these trees were alive just before the Flood 4,500 years ago. In other words, it is assumed that C-14 atoms were produced at the same rate in the earth’s atmosphere 4,500 years ago as they are today. But this assumption is demonstrably incorrect.

C-14 atoms are produced from nitrogen atoms in the earth’s upper atmosphere today as a result of the bombardment of the earth by cosmic rays from outer space. However, the earth is partially shielded from the full brunt of this cosmic ray bombardment by its magnetic field.13 Furthermore, the earth’s magnetic field is known from real-time historical measurements to have been stronger in the past, such that 1,400 years ago it would have been twice as strong as it is today.14 Therefore, if the earth’s magnetic field was twice as strong 1,400 years ago, then the production of C-14 atoms in the earth’s atmosphere would have been half of what it is today. This evidence for a stronger magnetic field in the past is also confirmed by measurement of the magnetism “fossilized” in ancient pottery.15 Therefore, since the amount of C-14 atoms in the atmosphere was much less back at the time of the Flood and beforehand due to a stronger magnetic field, then these C-14 dates for these fossilized woods, calculated assuming the same number of C-14 atoms available in the atmosphere back then as today, would be grossly inflated, as confirmed by the results in Table 2.

Additionally, animals and plants were far more prolific in the pre-Flood world than in today’s world. We know this from the huge quantities of plants buried in today’s coal beds and from the incredible numbers of creatures found fossilized in limestones and other rock layers in the geologic record of the Flood. Studies indicate that the amount of carbon in the animals and plants of the pre-Flood world could have been 300–700 times more than that in our present world.16 And the vast majority of this carbon would have been normal C-12, which would have swamped whatever small amount of C-14 was present in the pre-Flood world. In other words, the C-14/total-C ratio in the plants and animals of the pre-Flood world would have been 300–700 times smaller than the same ratio today. Thus C-14 ages calculated assuming the C-14/total-C ratio found today, rather than using the 300–700 times smaller ratio of the pre-Flood world, would be grossly inflated. This is exactly what we find in the C-14 ages provided by conventional radiocarbon laboratories of samples of pre-Flood wood fossilized in Flood rock layers and coal beds.

Conclusion

If the wooden remains of the Ark were to be found on Mt. Ararat, then samples of that wood would be expected to yield C-14 dates of between 20,000 years and 50,000 years, consistent with the C-14 dates of pre-Flood wood found fossilized in the geologic record of the Flood. Even though the true age of such fossilized pre-Flood wood should be only 4,500 years or so old, around the date for the biblical Flood, these grossly inflated C-14 dates obtained in conventional radiocarbon dating laboratories are due to those laboratories ignoring the very much less C-14 in the pre-Flood world compared to today’s world. But in strong contrast, the wood samples that have been claimed by a Chinese-Turkish team to have supposedly come from their discovery of the wooden remains of the Ark on Ararat have yielded C-14 dates from analyses in conventional radiocarbon laboratories ranging from recent (modern) to 6,891±4,647 years. These results are grossly short of what the C-14 dates should be for pre-Flood wood. Therefore, if we logically follow the soundest scientific inference, it must be concluded that these wood samples cannot have come from the pre-Flood wood used to build the Ark. Given the present C-14 evidence, despite the tantalizing wooden remains the Chinese-Turkish team claims to have discovered on Mt. Ararat, such artifacts CANNOT have come from the Ark. So whatever they have found, they are NOT the remains of the Ark.

Appendix: The δ¹³C Parameter

As well as radioactive carbon, C-14, most carbon consists of two stable atoms of slightly different atomic masses. These are the carbon isotopes called C-12 and C-13. The difference in the atomic masses of these isotopes is sufficiently large to affect the rates of chemical reactions and physical processes in which compounds containing these isotopes participate. For example, plants preferentially absorb ¹²CO₂ (carbon dioxide) from the atmosphere during photosynthesis and discriminate against ¹³CO₂ and ¹⁴CO₂.17 This process is called fractionation, and during photosynthesis this fractionation of carbon isotopes causes plant tissues, including wood, to be depleted in C-14 relative to ¹²CO₂ of the atmosphere. Furthermore, during laboratory preparation of samples for analysis further isotopic fractionation can occur between carbon isotopes when after the harsh pre-treatment the purified carbon is combusted into carbon dioxide. Thus these effects introduce small but systematic errors into C-14 dates of organic matter such as wood.

These errors can be eliminated by measuring the isotopic composition of carbon in the samples to be dated by the C-14 method. This is done by measuring the C-13/C-12 ratio of samples by mass spectrometry, which is the same instrument being used to measure the C-14 content of samples in the accelerator mass spectrometer (AMS) method. Because fractionation is mass-dependent, C-14/C-12 fractionation will be twice as great as C-13/C-12 fractionation.

The atomic C-13/C-12 ratio in ordinary terrestrial carbon as measured on a mass spectrometer is 0.0112, which is an awkward number to deal with. Therefore, the isotope composition of carbon is expressed by the δ¹³C parameter, defined as the per mil (parts per thousand) difference between the C-13/C-12 ratio of the sample and a carbon standard.18 The carbon-isotope standard chosen and used is carbon dioxide prepared from the internal calcite (calcium carbonate) skeleton (shell) of a Cretaceous belemnite (cephalopod) originally collected from the Peedee Formation in South Carolina. The C-13/C-12 fractionation is therefore normally expressed in the δ¹³C parameter relative to this PeeDee Belemnite (PDB) standard.

This fractionation factor or δ¹³C parameter is then used to correct C-14 dates. Since plants are depleted in C-13 (that is, enriched in C-12), their δ¹³C values are negative, whereas the δ¹³C values of marine carbonates are close to zero because their C-13/C-12 ratios are similar to those of PDB, which is also a marine carbonate.19 Because “modern wood” is established as the reference point for calibrating the efficiency of C-14 counting equipment, such as the accelerator mass spectrometer, date corrections must be applied relative to this type of material, which has a normal or “calibration” value of δ¹³C of -25 per mil (‰) relative to PDB.

Because there can be some variations in plants and woods, the δ¹³C value in recent and fossil wood samples can vary, as can be seen in the δ¹³C value for samples A, B and C in Table 1. Variations can also be seen in the δ¹³C values measured on the same sample in different laboratories, as can be seen in Table 1, where there is a 1.3‰ difference in the δ¹³C value determined on sample B in Laboratory 1 and Laboratory 2. Nevertheless, these laboratories verified that these were indeed wood samples they were C-14 dating, because the δ¹³C values they measured were within the range for recent and fossil woods.