Dating Methods

Alan Feuerbacher

Geological dating methods have long been a thorn in the Society's collective side. This is mainly due to its contention that the creative days of Genesis were precisely 7000 years long. This section establishes that geological dating methods are reasonably accurate, and just as important, are consistent with one another.

Radioisotope dating of fossil beds and geological events points to an explosion of life at the beginning of the Cambrian period about 600 million years ago. A line of evidence totally independent of radioisotope dating methods is consistent with this chronology, and provides independent confirmation of the validity radioisotope dating. This is consistent with the Bible principle that "at the mouth of two or three witnesses every matter may be established." How To Deep-Freeze a Mammoth⁵¹ explains:

Typical coral animals live inside a small cup made of lime that the animal itself builds up. New lime is deposited every day during the coral animal's lifetime. This happens only during daylight, for the coral lives in symbiotic relationship with a plant that needs sunlight for its life processes. When the deposition of lime ceases for the night, a growth line is formed which can be seen under a microscope. Analogous differences between summer and winter make it possible to distinguish annual growth lines, each of which contains 365 24-hour lines. Moreover it seems that the monthly four-week period may be reflected in the growth of the corals that live in areas where they are affected by changes in the tides. Such a coral skeleton thus becomes a kind of calendar, in which the passing of the days, the months, and the years can be read.

This is true not only of present-day corals. Similar growth lines also occur in fossil corals. In Scientific American (October 1966) the British scientist S. K. Runcorn describes corals from the Devonian period (for which radiometric age determinations give an age of about 400 million years). They, of course, are only distantly related to present-day corals (they belong to an extinct group called Rugosa). These corals from such an inconceivably distant past have the same daily, monthly, and annual rings as the modern ones. This indicates that the moon existed that long ago....

If we use the daily growth lines to calculate the number of days in the Devonian year, we find to our surprise that their number was around 400, rather than 365 as they decently ought to be.... If we look at somewhat younger (late Carboniferous, about 300 million years old) corals, the number of days in the year had been reduced to ca. 380 and in those of the present day they have of course come down to 365. So it seems that the earth is rotating ever more slowly on its axis. Other organisms besides corals give analogous evidence, with bivalves yielding particularly useful data for the time period from 350 million years ago to our day.

Actually scientists have known a long time that the rotation of the earth is slowing down, and in recent years it has even been possible to measure the retardation with the aid of the new atomic clocks. The retardation is caused by the friction effected by the tides. It is also possible to calculate how many days the Devonian year ought to have had, provided the friction over all these years has been the same as it is now -- that is, provided the moon has always retained its position [tidal friction has actually varied over time as continental drift has changed the configuration of oceans and continents]. The result was 399 days. So the correspondence is extremely close and we are forced to the conclusion that the same moon, our old friend, must have been there all the time.

As to the length of the day, an astronomy book⁵² says that

variations in the period of rotation of the earth have been detected by comparing the theory giving us the positions of such bodies as the moon and sun and certain planets with the actual observations of these positions. In addition, it is now possible to compare the unit of time as defined by the rotation of the earth with the unit defined by highly precise atomic clocks.... the slowing down in the rotation of the earth.... results in a lengthening of the day by 0.0016 second per century.

Creation and Evolution: Myth or Reality?⁵³ gives more details of the mechanism.

Studies of growth in fossil corals have made a fascinating contribution to geochronology involving past ocean tides and the inferred relationship between the earth and the moon. The moon pulls ocean water in a tidal bulge which moves westward as the earth rotates toward the east. The tidal drag acts as a brake on the spinning earth, gradually slowing it down. Early in the eighteenth century, Edmund Halley, Astronomer Royal of England, noted that there was a discrepancy between the recorded locations of ancient eclipses of the moon and their predicted places of observation. He pointed out that the differences could be resolved by assuming a slowing down of the rate of rotation of the earth. Modern astronomers have confirmed his theory, and by precise methods have found that the earth is now slowing at the rate of 0.002 seconds per century. This seems very little, but can be appreciable over tens of millions of years.

The slowing of the earth's spin decreases the number of days in the year and causes the moon to draw away from the earth, thus conserving the energy within the earth-moon system [actually it is the angular momentum that is conserved]. The rate of recession of the moon away from the earth is now calculated at about 5.6 centimeters per year. [This has been directly measured by laser ranging.] Until recently there was no way to test these astronomical deductions, but paleontology now provides an independent test.

The discovery was made by John W. Wells at Cornell University, a leading investigator of living and fossil corals. Wells knew that the skeletons of corals (and many other kinds of invertebrates) display parallel growth rings similar to the annual growth of trees. He was able to show that annual bands of living corals are themselves made of narrow lines which closely correspond to one day's growth.

With his fossil corals, he reported in 1963 that specimens of Devonian age averaged about 400 lines per year, and Carboniferous corals about 380. Subsequent investigations by intrigued paleontologists have shown that the number of daily growth increments per year in corals and molluscs has indeed been decreasing through geological time.

Astronomers had already calculated that average tidal friction would allow 425 days per year in the Cambrian and 400 days per year for the Devonian. As well as providing evidence of close agreement between these two scientific approaches, John Wells' work also provides a measure of the antiquity of fossils in years, totally independent of radiometric methods.

Following up Wells' discovery, Colin T. Scrutton, of the British Museum (Natural History), found what appeared to be monthly bands in Devonian corals equivalent to the intervals between times of the full moon. He calculated 13.03 lunar months in a Devonian year of 399 days. This work has opened up a whole new field of historical research involving the earth-moon relationship.

See Plate Tectonics & Crustal Evolution⁵⁴ and Scientific American, October, 1982, p. 170, for more a technical presentation. These works show the effect of changing tidal friction on day length as the continents have drifted around.

The above discussion shows that two independent lines of evidence, radioisotope and biological/astronomical, point to similar dates for when ancient corals and molluscs existed. The probability that both could be wrong by the same amount is very low. If this is not compelling evidence of the overall reliability of radioisotope dating methods, I don't know what else could be expected.

The Society often prints articles or reports that try to discredit radioactive dating or other geological methods, when these methods point to conclusions that contradict what the Bible or the Society say about some matter. These articles always show that one specific measurement, say a particular date, can be in error by a large amount. But they rarely show that the body of measurements as a whole, or the method itself, is wrong. It is easy to show that in many cases a single measurement can be wrong, but it is much harder to show that many measurements, which as a group point to a particular conclusion, are wrong. This is especially true when two or more independent methods point to similar conclusions. Even an ardent "scientific creationist" like Henry Morris, author of The Genesis Flood, in a discussion of radioactive dating methods, admits this:

Furthermore, it will be maintained that even though any given age measurement may be completely erroneous due to leaching or emanation or some other effect, there are many cases now known where the age estimate has been checked by two or more different methods, independently. It would seem improbable that the elements concerned would have each been altered in such a way as to continue to give equal ages; therefore, such agreement between independent measurements would seem to be strong evidence that alteration had not occurred and that the indicated age is therefore valid.⁵⁵

Large bodies of geological data which point to certain conclusions have been assembled by scientists. Some of the data are certainly wrong, as are some of the conclusions. But picking out one wrong thing here and there does not invalidate the entire set of conclusions. It must be shown how the preponderance of evidence points to different conclusions. This cannot be done using the sweeping generalities found in most of the Society's publications.

To illustrate more clearly what I'm getting at, suppose you are given the problem of figuring out what a large color painting represents, but you are never allowed to see it directly. You must examine it using only a light meter that measures color. The original is hidden behind a screen, which has a tiny, movable hole in it. You plug the light meter in the hole, move it around and take readings. You have been further told the painting is partly destroyed, and the light meter sometimes gives incorrect readings. You are to measure the color of the painting at a large number of points, and then paint a corresponding dot on another canvas. You will never know if any given dot correctly represents the original painting -- some dots will be garbage. But as you proceed, a recognizable image will emerge, and eventually you will be able to describe the original painting. Note that only if a pattern were there to begin with, and the light meter was reasonably reliable, could you make sense of the reconstruction.

Scientists face the same sort of problem in making measurements and drawing conclusions. When many observations using disparate measuring techniques lead to a conclusion, it is probably correct. With radioisotope dating, any given date may be bad, but when a large number of measurements point to a particular date, it will be wrong only if the dating method is itself fundamentally wrong. If a measurement technique yields random dates, no sense at all could be made of a large number of them. If the method has a built-in bias, then that will show up, but at least some sense will be able to be made out of it. By bias I mean that most dates will be off by a fixed amount of time or by a fixed percentage. In that case, if a second type of dating method yields the same results, it is extremely unlikely that both methods are incorrect. There are just too many ways things can go wrong. It is true that scientists sometimes use extremely sparse data to extrapolate to unwarranted conclusions, but with radioactive dating methods the data is profuse.

For example, the eruption of Mount Mazama that formed Crater Lake in Oregon had been dated by the mid-1960s by radiocarbon methods to between 6500 and 7000 years ago. A direct count of layers in ice cores from Greenland, in which ash from the eruption was found, gave a date of 4401 B.C., or 6391 years ago, not all that far from the radiocarbon dates, and in fact consistent with findings from tree ring studies that radiocarbon dates tend to be somewhat older than actual dates. Human artifacts have been found under ash from this eruption. A 1979 Scientific American article said:⁵⁶

.... tests showed that tephra layers found at certain archaeological sites came from Mount Mazama.... One of the archaeological sites was Fort Rock Cave.... Under the tephra [were] found sandals made of sagebrush bark, one of which was dated by carbon-14 analysis and found to be some 9000 years old.

Later the article mentions that the bulk of dating evidence put the eruption date at about 5000 B.C. The article also talks about the eruption of a volcano in the Mediterranean:

In the eastern Mediterranean the volcano Thera, on an island in the Aegean Sea, erupted in about the middle of the 15th century B.C., spreading tephra southeastward over an area that includes Crete. At that time Crete was the center of the Minoan civilization.... Archaeological excavations have revealed that the Minoan culture declined and disappeared suddenly after about 1450 B.C. Archaeologists have been puzzled by the unusual suddenness of the collapse, and when the approximate date of the Thera eruption became known, it was proposed that the tephra fall was the cause.... One carbon-14 date shows that the volcano probably erupted between 1499 and 1413 B.C., but [an investigator] found tephra from Thera in Minoan buildings that had been abandoned and covered by about 1500 B.C., according to the dating of artifacts in the area. The mystery will not be solved until more accurate dates are available.

The mystery had more light shed on it during the 1980s. The New York Times, August 9, 1981 reported on the activities of Danish, Swiss, and American scientists who had penetrated more than a mile deep into the ice cap in southern Greenland at a point named Dye 3. From winter-summer variations in the preserved frozen core, the drillers were able to read the year-by-year weather for the past 11,000 years. The article published a chart showing a volcanic explosion in 1390 B.C. that may have been one of several that spelled the end of the volcanic isle of Thera in the Aegean. These and related discoveries were also described in National Geographic.⁵⁷

Exploring Our Living Planet added more information:⁵⁸

By 1984, a University of Arizona team working with bristlecone pines, the oldest trees known, announced that their tree rings put the eruption at a startlingly early 1628-26 B.C. In 1985 scientists from the Smithsonian Institution reported finding grains of volcanic ash, apparently from Thera, in Nile Delta sediment. The ash lay at a depth corresponding to the early 16th century B.C.

In 1987 some Danish scientists weighed in with findings from distant Greenland: a trace of ash in the layered ice cap that would put the eruption still earlier, near 1645 B.C.

And in 1988, ancient trees preserved in Irish bogs confirmed the bristlecone chronology, yielding a single probable year: 1628 B.C.

So here we have a case where six dating methods -- archaeological, radioisotope, tree ring, bog deposit, river deposit and ice core studies -- point to ages within 7% of each other. Note that three of them are independent of one another -- archaeological, radioisotope and ice core layer counts.

The two examples I've just mentioned well attest to the overall accuracy of radiocarbon dating, both before and after the date of the Flood.

The 1986 Awake! series of articles⁵⁹ "Scientific Dates for Prehistoric Times," etc., is a prime example of the type of reasoning where a small number of instances of difficulty are used to show that the general case is incorrect. Many facts and figures are given showing how the various methods of dating may have serious problems in any particular case, but it is not shown how the methods can show overall consistency and yet be fundamentally wrong. For example, there are many events attributed to the close of the last ice age that are dated to about 11,000 years ago, usually by radiocarbon dating. But if radiocarbon dating is so prone to huge errors, how is it that any consistency can be found, and why does the 11,000 year figure keep showing up? If radiocarbon dating is so bad, why do other dating methods, such as direct count of ice cores in Greenland and Antarctica, give similar results?

See the section below, "More Evidence for the Ice Ages," for more details on ice cores, up to date as of July, 1993.

The Awake! series on geological dating says in conclusion, on page 27,

How do the results of scientific dating affect our understanding of the Bible?.... if we understand that the days of Genesis were long periods of thousands of years, with billions of years prior thereto for planet Earth's formation, there is no problem.... We have seen that geologists find generally good support in radiometric dating for their theories on the history of the earth, although most of the dates are far from certain.... We can confidently stand on this fact: The chronology in the Bible stands unimpeached by any scientific dating.

This, of course, ignores the fact that geologists' "theories on the history of the earth" say that the history of life goes back at least 600 million years and probably 3 billion, mountain ranges containing fossils go back hundreds of millions of years, etc. These are most assuredly not dated only thousands of years ago. I agree this does not contradict Bible chronology, as the Bible says nothing about dates prior to man's creation, but the Society's longstanding chronology of 34,000 years for the history of life is certainly contradicted.

Perhaps the Society should reexamine its position that the creative days were only 7000 years long. That position is no more tenable than the creationist claim that most sedimentary rocks of the world were formed in the Flood, which the Society no longer holds. Interestingly, the Society bases this idea ultimately on an old tradition that the seventh creative day of Genesis is itself 7000 years long, and that the Messiah would reign during the final 1000 years of it. The Society's founder C. T. Russell recognized this tradition in The Time Is At Hand, 1889, saying on page 39:

And though the Bible contains no direct statement that the seventh thousand will be the epoch of Christ's reign, the great Sabbath Day of restitution to the world, yet the venerable tradition is not without reasonable foundation.

That this is indeed an old tradition is shown by its inclusion in the New Testament apocryphal book (probably 1st century A.D.) The Epistle of Barnabas, Ch. 13. It seems the Society has forgotten its founder's view on the matter.

Occasionally a Watchtower publication omits critical information or uses dubious information to prove a point about dating methods or other topics related to science. For example, the Creation book said on page 96 that:

Biblical chronology indicates that a period of about 6,000 years has passed since the creation of humans. Why, then, does one often read about far longer periods of time since acknowledged human types of fossils appeared?

Before concluding that Bible chronology is in error, consider that radioactive dating methods have come under sharp criticism by some scientists. A scientific journal reported on studies showing that "dates determined by radioactive decay may be off -- not only by a few years, but by orders of magnitude." It said: "Man, instead of having walked the earth for 3.6 million years, may have been around for only a few thousand."

Upon checking this reference, which was to Popular Science magazine, I found the Society is not entirely honest with its readers on four counts. First, Popular Science is by no stretch of the imagination a "scientific journal." One could equally refer to The National Enquirer as a news journal. Referring to Popular Science this way is an attempt to lend "scientific authority" to a publication that has none. I realized by the time I was thirteen that Popular Science is not a "scientific journal." Second, the Popular Science article is mostly about the success of various dating methods, and only in the last few paragraphs is space given to the views of a single physicist, Robert Gentry, who dissents from the usual view. Third, the fact the dissenter is a Seventh Day Adventist, and a creationist who believes the universe was created in six literal days is not made clear. Statements from six-literal-day creationists regarding the accuracy of radioactive dating ought to be viewed like comments from Richard Nixon that politicians never lie. Fourth, the article's statement that man "may have been around for only a few thousand years" is merely a conclusion the article points out can be drawn from the views of Robert Gentry. It is not a conclusion the magazine itself, using its editorial voice, is making -- but Creation makes it appear it is. The reader gets the impression the article presents much scientific evidence showing radioactive dating is on shaky ground. But simply reading the Popular Science article shows that is not what it's about. Here are some excerpts from the article. Judge for yourself whether Creation gives a correct view to its readers. Better yet, read the article yourself.

So, today, everything -- human artifacts, animal remains, ancient rocks -- can be dated fairly accurately. The dates may be off a little, but that's mainly a matter of impurities in the sample or need to refine techniques, say the scientists involved.

Yet major mysteries and curious anomalies remain -- the odd speculations advanced by Columbia Union College's Robert Gentry, for instance.

Physicist Gentry believes that all of the dates determined by radioactive decay may be off -- not only by a few years, but by orders of magnitude.

His theory revolves around "halos," tiny, ringlike discolorations found within coalified wood (wood on its way to becoming coal) and mica, often in the proximity of radioactive uranium or thorium. Some halos can be explained in terms of conventional radioactive decay. Others, known as giant halos, cannot. They're simply too big to be caused by alpha particles thrown off by known isotopes, and they don't fit into any accepted theory. If the theory of radioactive decay is weak in one spot, says Gentry, doubt is cast on whatever answers isotopes give you.

Further, when Gentry studies halos in coalified wood, he finds that the uranium/lead ratios are often not at all what they should be. "Since the coalified wood was obtained from deposits supposedly at least tens of millions of years old," he says, "the ratio between uranium-238 and lead-206 should be low." They're not. They're so high, in fact, that "presently accepted ages may be too high by a factor of thousands." And man, instead of having walked the earth for 3.6 million years, may have been around for only a few thousand. "The possibility of reducing the 4.5-billion-year history of earth by a factor of a thousand," he says with some ire, "has not yet been seriously considered."

Most scientists simply dismiss the idea. As one physicist told me, "You can believe it or not; I don't."

"I realize it's difficult to believe," counters Gentry. "It would invalidate the whole underlying principle of radioactive dating: that the rates of decay are forever unvarying -- an untestable assumption."⁶⁰

Some research on Robert Gentry turned up the following:⁶¹

Mr. Gentry's findings were published almost ten years ago and have been the subject of some discussion in the scientific community. The discoveries have not, however, led to the formulation of any scientific hypothesis or theory which would explain a relatively recent inception of the earth or a worldwide flood. Gentry's discovery has been treated as a minor mystery which will eventually be explained. It may deserve further investigation, but the National Science Foundation has not deemed it to be of sufficient import to support further funding.

Here are some other comments, from physicist and professor of science history, Stephen G. Brush, concerning a number of points of scientific creationist criticism, including Robert Gentry's, of radioactive dating:⁶²

7. The existence of primordial polonium 218 halos in minerals indicates that the earth was not formed gradually over a long period of time but was created in a few hours "by Fiat nearly 6 millenia ago" (see Gentry 1979).

According to Gentry, the halos he has observed in certain minerals were produced by the decay of primordial polonium 218, an isotope with a half life of only three minutes. If his interpretation were correct, it would imply that the earth was created in a few minutes, but Gentry presents no basis for a quantitative estimate of when this event occurred. While he has attempted to cast doubt on the long time scale based on radioactive dating, I have not found in any of his publications a criticism specific enough to call for a reply. There are alternative explanations for the halos that he attributes to primordial polonium (York 1979). In particular, Hashemi-Nezhad et al. (1979) showed experimentally that the diffusion of lead in mica can be rapid enough to explain the anomalous polonium halos. According to one of the experimenters in this group, "the haloes are inconsistent with creation less than tens to hundreds of millions of years ago unless one invents two easily observable but unobserved lead isomers of quite improbable characteristics" (Fremlin 1981).

Gentry does not claim that his results lead directly to a specific age for the earth, but he argues that the ratios of uranium 238 to lead 206 found in coalified wood from the Colorado Plateau could be explained by an infiltration of uranium a few thousand years ago (Gentry et al. 1976b, and telephone conversation, 16 September 1981). To accept his view that the infiltration event was associated with the creation of the earth would require discarding theories based on a large amount of data from many areas of science in order to explain a single isolated type of observation. It does not seem sensible to throw out well-established principles of science without having alternative principles that could explain at least most of the same observations, and no such alternative exists (Damon 1979; York 1979). This is a good illustration of the fact that no scientific theory can or must explain all observations and that a theory that is able to give satisfactory explanation of most observations will not be replaced unless a better one is available. Gentry's postulate of recent creation of the earth is contradicted by so many other facts that it has gained no support from other scientists who are familiar with this field. (See Dalrymple 1982a for further details on problems in Gentry and other creationists' critiques of radioactive dating.)

It should be evident by now that the Popular Science article's reference to "the odd speculations advanced by.... Robert Gentry" means precisely that. The Creation book's quotations from this article distort what it said.

In conclusion, it is clear that independent evidence, in the form of ancient coral growth rings and the slowing of the earth's rate of rotation, and in the form of ice cores, confirms the general validity of radioactive dating methods. To convincingly show these dating methods to be invalid, one must show how radioactive dating consistently shows errors, and show how independent methods that point to similar conclusions are also invalid. In particular it must be shown how two or more invalid methods can be consistent with one another. It is not sufficient to argue that "men make mistakes, so all scientific methods may be wrong," as the Society invariably does.

Footnotes

⁵¹ Bjorn Kurten, How To Deep-Freeze a Mammoth, pp. 23-24, Columbia University Press, New York, 1986. English Edition.

⁵² Lloyd Motz and Anneta Duveen, Essentials of Astronomy, p. 64, Wadsworth Publishing Company, Inc., Belmont, CA, 1966.

⁵³ Norman D. Newell, op cit, pp. 119-124.

⁵⁴ Kent C. Condie, Plate Tectonics & Crustal Evolution, Second Edition, pp. 19-20, Pergamon Press, Inc., New York, 1982.

⁵⁵ Henry M. Morris and John C. Whitcomb, The Genesis Flood, pp. 343-344, Baker Book House, Grand Rapids, Michigan, 1961.

⁵⁶ Laurence R. Kittleman, "Tephra," Scientific American, p. 171, New York, December, 1979.

⁵⁷ "Ice on the World," National Geographic Magazine, p. 98, Washington, D.C., January, 1987.

⁵⁸ Robert D. Ballard, Exploring Our Living Planet, p. 315, National Geographic Society, Washington, D.C., 1988.

⁵⁹ Awake!, pp. 17-27, Watchtower Bible and Tract Society of New York, Inc., Brooklyn, NY.

⁶⁰ Robert Gannon, "How Old Is It?," Popular Science, p. 81, November, 1979.

⁶¹ David B. Wilson, Did the Devil Make Darwin Do It?, p. 216, The Iowa State Press, Ames, Iowa, 1983.

⁶² Laurie R. Godfrey, Scientists Confront Creationism, pp. 71-72, W. W. Norton & Company, New York, 1983.