Paleontologists Try to Date the Fossils

Paleontologists have attempted to copy the geologists’ success in dating rocks only a few million years old. Some of their fossils, they believe, might fall in that age range. Alas, the potassium-argon clock does not work so well for them! Of course, fossils are not found in igneous rocks but only in sediments, and for these radiometric dating is usually not trustworthy.

An illustration of this is when fossils have been buried in a thick fall of volcanic ash that has later been consolidated to form a tuff. This is actually a sedimentary stratum, but it is made of igneous matter that solidified in the air. If it can be dated, it will serve to give the age of the fossil enclosed in it.

Such a case was found in the Olduvai Gorge in Tanzania, where fossils of apelike animals attracted special attention because their finders claimed they were linked to humans. First measurements of argon in the volcanic tuff in which the fossils were found showed an age of 1.75 million years. But later measurements at another qualified laboratory gave results a half million years younger. Most disappointing to evolutionists was the finding that the ages of other layers of tuff, above and below, were not consistent. Sometimes the upper layer had more argon than the one below it. But this is all wrong, geologically speaking​—the upper layer had to be deposited after the lower and should have less argon.

The conclusion was that “inherited argon” was spoiling the measurements. Not all the argon previously formed had been boiled out of the molten rock. The clock had not been set to zero. If only one tenth of 1 percent of the argon previously produced by the potassium was left in the rock when it melted in the volcano, the clock would be started with a built-in age of nearly a million years. As one expert put it: “Some of the dates must be wrong, and if some are wrong maybe all of them are wrong.”

Notwithstanding expert opinions that these dates may be quite meaningless, the original age of 1.75 million years for the Olduvai fossils continues to be quoted in popular magazines committed to evolution. They give the lay reader no warning that such ages are really no more than guesses.

The Radiocarbon Clock

It Dates Once-Living Remains. Or Does It?

ALL the foregoing clocks run so slowly that they are of little or no use in studying archaeological problems. Something much faster is needed to match the time scale of human history. This need has been met by the radiocarbon clock.

Carbon 14, a radioactive isotope of ordinary carbon 12, was first found in atom-smashing experiments in a cyclotron. Then it was found also in the earth’s atmosphere. It emits weak beta rays, which can be counted by a suitable instrument. Carbon 14 has a half-life of only 5,700 years, which is suitable for dating things associated with man’s early history.

The other radioactive elements we have discussed have lives that are long compared to the earth’s age, so they have existed since earth’s creation down to the present day. But radiocarbon has such a short life, relative to the earth’s age, that it can still be here only if it has been continually produced in some way. That way is the bombardment of the atmosphere by cosmic rays, which convert nitrogen atoms into radioactive carbon.

This carbon, in the form of carbon dioxide, is used by plants in the process of photosynthesis and is converted into all kinds of organic compounds in living cells. Animals and, yes, we humans, eat the plant tissues, so everything that lives comes to contain radiocarbon in the same proportion as it is found in the air. As long as anything lives, the radiocarbon in it, which decays, is replenished by fresh intake. But when a tree or an animal dies, the supply of fresh radiocarbon is cut off, and the radiocarbon level in it begins to drop. If a piece of wood charcoal or an animal bone is preserved for 5,700 years, it will contain only half as much radiocarbon as it had when alive. So, in principle, if we measure the proportion of carbon 14 remaining in something that once was alive, we can tell how long it has been dead.

The radiocarbon method can be applied to a wide variety of things of organic origin. Many thousands of samples have been dated by it. Their fascinating diversity is suggested by just a few examples:

Wood from the funerary ship found in the tomb of Pharaoh Seostris III was dated at 1670 B.C.E.

Heartwood from a giant redwood in California, which had 2,905 annual rings when it was cut down in 1874, was dated at 760 B.C.E.

Linen wrappings from the Dead Sea Scrolls, dated to the first or second century B.C.E. by the style of handwriting, were measured by the radiocarbon content to be 1,900 years old.

A piece of wood found on Mt. Ararat, and considered by some to be possibly from Noah’s ark, proved to date only from 700 C.E.​—old wood, indeed, but not nearly old enough to predate the Flood.

Woven rope sandals dug out of volcanic pumice in an Oregon cave showed an age of 9,000 years.

Flesh from a baby mammoth, frozen in Siberian muck for thousands of years, was found to be 40,000 years old.

How reliable are these dates?

Errors in the Radiocarbon Clock

The radiocarbon clock looked very simple and straightforward when it was first demonstrated, but it is now known to be prone to many kinds of error. After some 20 years’ use of the method, a conference on radiocarbon chronology and other related methods of dating was held in Uppsala, Sweden, in 1969. The discussions there between chemists who practice the method and archaeologists and geologists who use the results brought to light a dozen flaws that might invalidate the dates. In the 17 years since then, little has been accomplished to remedy these shortcomings.

One nagging problem has always been to ensure that the sample tested has not been contaminated, either with modern (live) carbon or with ancient (dead) carbon. A bit of wood, for example, from the heart of an old tree might contain live sap. Or if that has been extracted with an organic solvent (made from dead petroleum), a trace of the solvent might be left in the portion analyzed. Old buried charcoal might be penetrated by rootlets from living plants. Or it might be contaminated with much older bitumen, difficult to remove. Live shellfish have been found with carbonate from minerals long buried or from seawater upwelling from the deep ocean where it had been for thousands of years. Such things can make a specimen appear either older or younger than it really is.

The most serious fault in radiocarbon-dating theory is in the assumption that the level of carbon 14 in the atmosphere has always been the same as it is now. That level depends, in the first instance, on the rate at which it is produced by cosmic rays. Cosmic rays vary greatly in intensity at times, being largely affected by changes in the earth’s magnetic field. Magnetic storms on the sun sometimes increase the cosmic rays a thousandfold for a few hours. The earth’s magnetic field has been both stronger and weaker in past millenniums. And since the explosion of nuclear bombs, the worldwide level of carbon 14 has increased substantially.

On the other hand, the proportion is affected by the quantity of stable carbon in the air. Great volcanic eruptions add measurably to the stable carbon-dioxide reservoir, thus diluting the radiocarbon. In the past century, man’s burning of fossil fuels, especially coal and oil, at an unprecedented rate has permanently increased the quantity of atmospheric carbon dioxide. (More details on these and other uncertainties in the carbon-14 clock were given in the April 8, 1972, issue of Awake!)

Dendrochronology​—Dating by the Growth Rings of Trees

Faced with all these fundamental weaknesses, the radiocarbon people have turned to standardizing their dates with the help of wood samples dated by counting tree rings, notably those of bristlecone pines, which live hundreds and even thousands of years in the southwestern United States. This field of study is called dendrochronology.

So the radiocarbon clock is no longer regarded as yielding an absolute chronology but one which measures only relative dates. To get the true date, the radiocarbon date has to be corrected by the tree-ring chronology. Accordingly, the result of a measurement of radiocarbon is referred to as a “radiocarbon date.” By referring this to a calibration curve based on tree rings, the absolute date is inferred.

This is sound for as far back as the bristlecone ring count is reliable. The problem now comes up that the oldest living tree whose age is known goes back only to 800 C.E. In order to extend the scale, scientists try to match overlapping patterns of thin and thick rings in pieces of dead wood found lying nearby. By patching together 17 remnants of fallen trees, they claim to go back over 7,000 years.

But the tree-ring standard does not stand alone either. Sometimes they are not sure just where to put one of the dead pieces, so what do they do? They ask for a radiocarbon measurement on it and use that as a guide in fitting it in. It reminds one of two lame men with only one crutch between them, who take turns using it, one leaning for a while on his partner, then helping to hold him up.

One must wonder at the miraculous preservation of loose bits of wood lying so long in the open. It would seem they might have been washed away by heavy rainfall or picked up by passersby for firewood or some other use. What has prevented rot or insect attack? It is credible that a living tree might withstand the ravages of time and weather, an occasional one surviving for a thousand years or more. But dead wood? For six thousand years? It strains credibility. Yet this is what the older radiocarbon dates are based on.

Nevertheless, the radiocarbon experts and the dendrochronologists have managed to put aside such doubts and smooth over the gaps and inconsistencies, and both feel satisfied with their compromise. But how about their customers, the archaeologists? They are not always happy with the dates they get back on the samples they send in. One expressed himself this way at the Uppsala conference:

“If a carbon-14 date supports our theories, we put it in the main text. If it does not entirely contradict them, we put it in a footnote. And if it is completely ‘out of date,’ we just drop it.”

Some of them still feel that way. One wrote recently concerning a radiocarbon date that was supposed to mark the earliest domestication of animals:

“Archeologists [are coming] to have second thoughts about the immediate usefulness of radiocarbon age determinations simply because they come out of ‘scientific’ laboratories. The more that confusion mounts in regard to which method, which laboratory, which half-life value, and which calibration is most reliable, the less we archeologists will feel slavishly bound to accept any ‘date’ offered to us without question.”

The radiochemist who had supplied the date retorted: “We prefer to deal with facts based on sound measurements​—not with fashionable nor emotional archeology.”

If scientists disagree so sharply about the validity of these dates reaching back into man’s antiquity, is it not understandable that laymen might be skeptical about news reports based on scientific “authority,” such as those quoted at the head of this series of articles?

Direct Counting of Carbon 14

A recent development in radiocarbon dating is a method for counting not just the beta rays from the atoms that decay but all the carbon-14 atoms in a small sample. This is particularly useful in dating very old specimens in which only a tiny fraction of the carbon 14 is left. Out of a million carbon-14 atoms, only one, on the average, will decay every three days. This makes it quite tedious, when measuring old samples, to accumulate enough counts to distinguish the radioactivity from the cosmic-ray background.

But if we can count all the carbon-14 atoms now, without waiting for them to decay, we can gain a millionfold in sensitivity. This is accomplished by bending a beam of positively charged carbon atoms in a magnetic field to separate the carbon 14 from the carbon 12. The lighter carbon 12 is forced into a tighter circle, and the heavier carbon 14 is admitted through a slit into a counter.

This method, although more complicated and more expensive than the beta-ray-counting method, has the advantage that the amount of material needed for a test is a thousand times less. It opens up the possibility of dating rare ancient manuscripts and other artifacts from which a sample of several grams that would be destroyed in testing just cannot be had. Now such articles can be dated with just milligrams of sample.

One suggested application of this would be to date the Shroud of Turin, which some believe Jesus’ body was wrapped in for burial. If radiocarbon dating was to show that the cloth is not that old, it would confirm the suspicions of doubters that the shroud is a hoax. Until now, the archbishop of Turin has refused to donate a sample for dating because it would take too large a piece. But with the new method, one square centimeter would be enough to determine whether the material dates from the time of Christ or only from the Middle Ages.

In any event, attempts to extend the time range have little significance as long as the greater problems remain unsolved. The older the sample is, the more difficult it is to ensure the complete absence of slight traces of younger carbon. And the farther we try to go beyond the few thousand years for which we have a reliable calibration, the less we know about the atmospheric level of carbon 14 in those ancient times.

Several other methods have been studied for dating events in the past. Some of these are related indirectly to radioactivity, such as the measurement of fission tracks and radioactive halos.