No. 189 MYTHS REGARDING RADIOCARBON DATING

by Gerald E. Aardsma*

The field of radiocarbon dating has become a technical one far removed

from the naive simplicity which characterized its initial introduction by

Libby in the late 1940's. It is, therefore, not surprising that many mis-

conceptions about what radiocarbon can or cannot do and what it has

or has not shown are prevalent among creationists and evolutionists-lay

people as well as scientists not directly involved in this field. In the

following article, some of the most common misunderstandings regarding

radiocarbon dating are addressed, and corrective, up-to-date scientific

creationist thought is provided where appropriate.

Radiocarbon is not used to date the age of rocks or to determine the age

of the earth. Other radio metric dating methods such as potassium-argon

or rubidium-strontium are used for such purposes by those who believe

that the earth is billions of years old. Radiocarbon is not suitable for this

purpose because it is only applicable: a) on a time scale of thousands of

years and b) to remains of once-living organisms (with minor exceptions,

from which rocks are excluded).

Some organic materials do give radiocarbon ages in excess of 50,000

,radiocarbon years." However, it is important to distinguish between

,radiocarbon years" and calendar years. These two measures of time will

only be the same if all of the assumptions which go into the conventional

Dr. Aardsma is Chairman of the Astro/Geophysics Department in the ICR

Graduate School. He received his Ph.D. from the University of Toronto doing

research in accelerator mass spectrometry, a new technique now widely used

in radiocarbon dating.

radiocarbon dating technique are valid. Comparison of ancient, histori-

cally dated artifacts (from Egypt, for example) with their radiocarbon

dates has revealed that radiocarbon years and calendar years are not

the same even for the last 5,000 calendar years. Since no reliable histori-

cally dated artifacts exist which are older than 5,000 years, it has not

been possible to determine the relationship of radiocarbon years to

calendar years for objects which yield dates of tens of thousands of

radiocarbon years. Thus, it is possible (and, given the Flood, probable)

that materials which give radiocarbon dates of tens of thousands of

radiocarbon years could have true ages of many fewer calendar years.

MYTH #3. The shells of live freshwater clams have been radio-

carbon dated in excess of 1600 years old, clearly showing that the

radiocarbon dating technique is not valid.

The shells of live freshwater clams can, and often do, give anomalous

radiocarbon results. However, the reason for this is understood and the

problem is restricted to only a few special cases, of which freshwater

clams are the best-known example. It is not correct to state or imply

from this evidence that the radiocarbon dating technique is thus shown

to be generally invalid.

The problem with freshwater clams arises because these organisms

derive the carbon atoms which they use to build their shells from the

water in their environment. If this water is in contact with significant

quantities of limestone, it will contain many carbon atoms from dissolved

limestone. Since limestone contains very little, if any, radiocarbon, clam

shells will contain less radiocarbon than would have been the case if they

had gotten their carbon atoms from the air. This gives the clam shell an

artificially old radiocarbon age.

This problem, known as the "reservoir effect," is not of very great

practical importance for radiocarbon dating since most of the artifacts

which are useful for radiocarbon dating purposes and are of interest to

archaeology derive from terrestrial organisms which ultimately obtain

their carbon atoms from the air, not the water.

MYTH #4. Samples of coal have been found with radiocarbon

ages of only 20,000 radiocarbon years or less, thus proving the

recent origin of fossil fuels, probably in the Flood.

I am not aware of any authentic research which supports this claim.

Also, it does not coincide with what creationist scientists would currently

anticipate based upon our understanding of the impact of the Flood on

radiocarbon.

It is not difficult to see how such a claim could arise, however.

there are two characteristics of the instrumental measurement of radiocarbon

which, if the lay observer is unaware, could easily lead to such an idea.

First, any instrument which is built to measure radiocarbon has a

limit beyond which it cannot separate the signal due to radiocarbon in

the sample from the signal due to background processes within the measur-

ing apparatus. Even a hypothetical sample containing absolutely

no radiocarbon mall register counts in a radiocarbon counter because of

background signals within the counter. In the early days of radiocarbon

analysis this limit was often around 20,000 radiocarbon years. Thus, all

the researcher was able to say about samples with low levels of radio-

carbon was that their age was greater than or equal to 20,000 radio-

carbon years (or whatever the sensitivity limit of his apparatus was).

Some may have mistaken this to mean that the sample had been dated

to 20,000 radiocarbon years.

The second characteristic of the measurement of radiocarbon is that

it is easy to contaminate a sample which contains very little radiocarbon

with enough radiocarbon from the research environment to give it an

apparent radiocarbon age which is much less than its actual radiocarbon

age. For example, a sample with a true radiocarbon age of 100,000 radio-

carbon years will yield a measured radiocarbon age of about 20,000

radiocarbon years if the sample is contaminated with a weight of modern

carbon of just 5% of the weight of the sample's carbon. It is not too diffi-

cult to supply contaminating radiocarbon since it is present in relatively

high concentrations in the air and in the tissues of all living things in-

cluding any individuals handling the sample. For this reason special pre-

cautions need to be exercised when sampling materials which contain

only small amounts of radiocarbon.

Reports of young radiocarbon ages for coal probably all stem from a

misunderstanding of one or both of these two factors. Measurements

made using specially designed, more elaborate apparatus and more

astute sampling-handling techniques have yielded radiocarbon ages for

anthracite greater than 70,000 radiocarbon years, the sensitivity limit of

this equipment.

MVTH #5. Continuous series of tree-ring dated wood samples

have been obtained for roughly the past 10,000 years which give

the approximate correct radiocarbon age, demonstrating the

general validity of the conventional radiocarbon dating technique.

Several long tree-ring chronologies have been constructed specifically for

use in calibrating the radiocarbon time scale. By radiocarbon dating a

piece of wood which has been dated by counting the annual growth rings

of trees back to when that piece of wood grew, a calibration table can

be constructed to convert radiocarbon years to true calendar years. Of

course, the table, so constructed, will only give the correct calibration

if the tree-ring chronology which was used to construct it had placed each

ring in the true calendar year in which it grew.

Long tree-ring chronologies are rare (there are only two that I am

aware of which are of sufficient length to be of interest to radiocarbon)

and difficult to construct. They have been slowly built up by matching

ring patterns between trees of different ages, both living and dead, from

a given locality. As one might expect, the further back the tree-ring

chronology extends, the more difficult it becomes to locate ancient tree

specimens with which to extend the chronology. To alleviate this prob-

lem it seems, from the published literature, to be a common practice to

first radiocarbon date a large number of potential tree specimens and

then select those with appropriate radiocarbon age for incorporation into

the tree-ring chronology. Such a procedure introduces a bias into the

construction of the tree-ring chronology for the earliest millennia which

could possibly obscure any unexpected radiocarbon behavior.

it is not clear to what extent this circular process has influenced the

final tree-ring calibrations of radiocarbon. Efforts by creationist scientists

to obtain the raw data from which the oldest tree-ring chronology has

been constructed to investigate this possible source of bias have so far

not met with success. Until the raw data does become available for

general scrutiny, creationists are clearly justified in maintaining a high

degree of skepticism.

In any event, the calibration tables which have been produced from

tree rings do not support the conventional steady-state model of radio-

carbon which Libby introduced. Rather, they lend support to the

idea that significant perturbations to radiocarbon have occurred in the

past.

Creationists are interested in the truth. This involves exposing areas

of weakness and error in the conventional interpretation of radiocarbon

results as well as suggesting better understandings of radiocarbon con-

gruent with a Biblical, catastrophist, Flood model of earth history. At

ICR research into alternative interpretations of radiocarbon which are

not in conflict with the Biblical record of the past continue to be actively

pursued and a special radiocarbon laboratory is being developed for

research into the method.

Radiocarbon holds unique potential for the student of earth history

who adheres to a recent creation, It is doubtful that other radio metric

dating techniques such as potassium-argon or rubidium-strontium will

ever be of much value or interest to the young-earth creationist who

desires to develop further our understanding of the past because they

are only applicable on a time scale of millions or billions of years. Radio-

carbon, however, is applicable on a time scale of thousands of years. A

proper understanding of radiocarbon will undoubtedly figure very signifi-

cantly into the unraveling of such questions as when (and possibly why)

the mammoths became extinct, the duration of the glacial period follow-

ing the Flood, and the general chronology of events from the Flood to

the present.

Creationists are not so much interested in debunking radiocarbon as

we are in developing a proper understanding of it to answer many of our

own questions regarding the past. At the present time it appears that the

conventional radioc,,rbon dating technique is on relatively firm ground

for dates which fall within the past 3,000 years. For periods of time prior

to this, there are legitimate reasons to question the validity of the

conventional results and seek for alternative interpretations.