Answers to Creationist Attacks on Carbon-14 Dating
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-14) 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-14 dating, using the question-answer format that has proved so useful to lecturers and debaters.
Question: How does carbon-14 dating work?
Answer: Cosmic rays in the upper atmosphere are constantly converting the isotope nitrogen-14 (N-14) into carbon-14 (C-14 or radiocarbon). Living organisms are constantly incorporating this C-14 into their bodies along with other carbon isotopes. When the organisms die, they stop incorporating new C-14, and the old C-14 starts to decay back into N-14 by emitting beta particles. The older an organism's remains are, the less beta radiation it emits because its C-14 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-14 decays with a half-life of 5,730 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-14 dating. How do you reply?
Answer: It does discredit the C-14 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-14 because these sources are so old and have not been mixed with fresh carbon from
the air. Thus, a freshly killed mussel has far less C-14 than a freshly killed something else, which is why the C-14 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-14. 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-14. 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-14, enough to give them C-14 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-14 left that their beta radiation is swamped out by the background radiation of cosmic rays and potassium-40 (K-40) 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-14 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. (p. 108)
Cosmic rays form beta radiation all the time; this is the radiation that turns N-14 to C-14 in the first place. K-40 decay also forms plenty of beta radiation. Stearns, Carroll, and Clark point out that ". . . this isotope [K-40] accounts for a large part of the normal background radiation that can be detected on the earth's surface" (p. 84). 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 (1966) claim that cosmic radiation is now forming C-14 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-14 the atmosphere had. If we extrapolate
as far back as ten thousand years ago, we find the atmosphere would not have had any C-14 in it at all. If they are right, this means all C-14 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. How do you reply?
Answer: Yes, Cook is right that C-14 is forming today faster than it's decaying. However, the amount of C-14 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 6200 BC, one can check out the C-14 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 8,200-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-14 dates, they find that radiocarbon ages before 1000 BC are really too young—not too old as Cook maintains. For example, pieces of wood that date at about 6200 BC by tree-ring counts date at only 5400 BC by regular C-14 dating and 3900 BC by Cook's creationist revision of C-14 dating (as we see in the article, "Dating, Relative and Absolute," in the Encyclopaedia Britannica). So, despite creationist claims, C-14 before three thousand years ago was decaying faster than it was being formed and C-14 dating errs on the side of making objects from before 1000 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. Such multiple growth rings are extremely rare in bristlecone pines, however, and they are especially infrequent at the elevation and latitude (37� 20' N) of the sites being studied. 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. (p. 840)
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 1250 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 6200 BC. (See Renfrew for more details.)
So, creationists who complain about double rings in their attempts to disprove C-14 dating are actually grasping at straws. If the Flood of Noah occurred around 3000 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-14 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-14 would have been produced. Therefore, any C-14 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 4000 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. V. 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 1.5 times as strong as today around 1 AD, 1.6 times as strong around 400 BC, 0.8 times as strong around 2000 BC, and only 0.5 times as strong around 4000 BC. (See Bailey, Renfrew, and Encyclopedia Britannica for details.) In other words, it rose in intensity from 0.5 times its present value in 4000 BC to a peak of 1.6 times its present value in 400 BC, and it has been slowly declining since then. Even before the bristlecone pine calibration of C-14 dating was worked out by Ferguson, Bucha predicted that this change in the magnetic field would make radiocarbon dates too young.
This idea [that the fluctuating magnetic field affects influx of cosmic rays, which in turn affects C-14 formation rates] has been taken up by the Czech geophysicist, V. Bucha, who has been able to determine, using samples of baked clay from archeological sites, what the intensity of the earth's magnetic field was at the time in question. Even before the tree-ring calibration data were available to them, he and the archeologist, Evzen Neustupny, were able to suggest how much this would affect the radiocarbon dates. (Renfrew, p. 76)
Not only that, but his predictions were confirmed in detail:
There is a good correlation between the strength of the earth's magnetic field (as determined by Bucha) and the deviation of the atmospheric radiocarbon concentration from its normal value (as indicated by the tree-ring radiocarbon work). (Renfrew, p. 76)
So, once we know all the magnetic data, we see that it really supports the tree-ring
calibration of C-14 dating, rather than the conclusions of Cook and Barnes.
As for the question of polarity reversals, plate tectonics can teach us much. It is a fact that new oceanic crust continually forms at the mid-oceanic ridges and spreads away from those ridges in opposite directions. When lava at the ridges hardens, it keeps a trace of the magnetism of the earth's magnetic field. Therefore, every time the magnetic field reverses itself, bands of paleomagnetism of reversed polarity show up on the ocean floor alternated with bands of normal polarity. These bands are thousands of kilometers long, they vary in width, they lie parallel, and the bands on either side of any given ridge form mirror images of each other. Thus it can be demonstrated that the magnetic field of the earth has reversed itself dozens of times throughout earth history.
Barnes, writing in 1973, ought to have known better than to quote the gropings and guesses of authors of the early sixties in an effort to debunk magnetic reversals. Before plate tectonics and continental drift became established in the mid-sixties, the known evidence for magnetic reversals was rather scanty, and geophysicists often tried to invent ingenious mechanisms with which to account for this evidence rather than believe in magnetic reversals. However, by 1973, sea floor spreading and magnetic reversals had been documented to the satisfaction of almost the entire scientific community. Yet, instead of seriously attempting to rebut them with up-to-date evidence, Barnes merely quoted the old guesses of authors who wrote before the facts were known. But, in spite of Barnes, paleomagnetism on the sea floor conclusively proves that the magnetic field of the earth oscillates in waves and even reverses itself on occasion. It has not been decaying exponentially as Barnes maintains.
Question: Does outside archaeological evidence confirm theC-14 dating method?
Answer: Yes. When we know the age of a sample through archaeology or historical sources, the C-14 method (as corrected by bristlecone pines) agrees with the age within the known margin of error. For instance, Egyptian artifacts can be dated both historically and by radiocarbon, and the results agree. At first, archaeologists used to complain that the C-14 method must be wrong, because it conflicted with well-established archaeological dates; but, as Renfrew has detailed, the archaeological dates were often based on false assumptions. One such assumption was that the megalith builders of western Europe learned the idea of megaliths from the Near-Eastern civilizations. As a result, archaeologists believed that the Western megalith-building cultures had to be younger than the Near Eastern civilizations. Many archaeologists were skeptical when Ferguson's calibration with bristlecone pines was first published, because, according to his method, radiocarbon dates of the Western megaliths showed them to be much older than their Near-Eastern counterparts. However, as Renfrew demonstrated, the similarities between these Eastern and Western cultures are so superficial that
the megalith builders of western Europe invented the idea of megaliths independently of the Near East. So, in the end, external evidence reconciles with and often confirms even controversial C-14 dates.
One of the most striking examples of different dating methods confirming each other is Stonehenge. C-14 dates show that Stonehenge was gradually built over the period from 1900 BC to 1500 BC, long before the Druids, who claimed Stonehenge as their creation, came to England. Astronomer Gerald S. Hawkins calculated with a computer what the heavens were like back in the second millennium BC, accounting for the precession of the equinoxes, and found that Stonehenge had many significant alignments with various extreme positions of the sun and moon (for example, the hellstone marked the point where the sun rose on the first day of summer). Stonehenge fits the heavens as they were almost four thousand years ago, not as they are today, thereby cross-verifying the C-14 dates.
Question: What specifically does C-14 dating show that creates problems for the creation model?
Answer: C-14 dates show that the last glaciation started to subside around twenty thousand years ago. But the young-earth creationists at ICR and elsewhere insist that, if an ice age occurred, it must have come and gone far less than ten thousand years ago, sometime after Noah's flood. Therefore, the only way creationists can hang on to their chronology is to poke all the holes they can into radiocarbon dating. However, as we have seen, it has survived their most ardent attacks.
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Barnes, Thomas G. 1973. Origin and Destiny of the Earth's Magnetic Field. San Diego: Creation-Life Publishers.
Cook, Melvin A. 1966. Prehistory and Earth Models. London: Max Parrish and Co., Ltd.
"Dating, Relative and Absolute." Encyclopaedia Britannica: Macropaedia, Vol. 5. 1974.
"Earth, Magnetic Field of." Encyclopaedia Britannica: Macropaedia, Vol. 5. 1974.
Fergusson, C. W. 1968. "Bristlecone Pine: Science and Aesthetics." Science 159:839-846.
Hawkins, Gerald S. 1965. Stonehenge Decoded. New York: Doubleday & Co.
Hurley, Patrick M. 1959. How Old Is the Earth? New York: Doubleday & Co.
Kieth, M. C., and Anderson, G. M. August 16, 1963. "Radiocarbon Dating:
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