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
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
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
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
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.