Note: This article by Robert H. Brown and two more to be published in the March and April issues of this journal, are reproduced from the book Genesis and Science by Harold G. Coffin
It is common knowledge that radiocarbon laboratories have determined ages for organic material which in a vast number of cases appear to be in conflict with the specifications concerning earth history given by the book of Genesis and endorsed by the Gospel writers and the apostle Paul in the New Testament. There is an evident need for intensive and careful study in the broad field of radiocarbon dating in order to find the agreement that we have been assured exists between the book of nature and the written Word.
In approaching any body of scientific literature it is well to keep in mind the unavoidable tendency of an investigator to harmonize the information available to him with his general world view. The human mind is designed to integrate and summarize its observations into generalized principles and viewpoints. This characteristic is necessary for the development of understanding and capability. As a consequence of their cultural and educational background, most of the radiocarbon specialists have a world view that is based on uniformitarianism and progressive evolutionary development of life. In the treatment of some of the information provided by carbon-14 analysis, the seeker for truth who begins with commonly accepted uniformitarian viewpoints may experience a more difficult and devious path toward a fuller understanding than would have been the case if his initial viewpoints had conformed with the guidelines set forth in the Bible. Where scientific observation relates to divinely inspired testimony, we have been assured that an honest search for truth will result in both increased understanding and in confirmation of the inspired testimony.
One who becomes acquainted with the individuals who are leading out in the development and application of carbon-14 dating techniques finds them to be men and women of high ideals who are intensely devoted to finding truth in their areas of investigation and are meticulous in maintaining a distinction between speculation and firmly substantiated evidence. With carbon-14 dating, as also with many other areas of human thought, the dogmatism with which speculative conclusions are advocated commonly increases with the distance one goes from prime sources of information.
The Formation of Carbon-14
Before considering some recent developments on radiocarbon dating, many readers may appreciate a brief survey of the physical phenomena involved. Stars eject into space some of the matter of which they are composed. This ejected matter represents the chemical composition of its parent star and, consequently, is made up of hydrogen, small amounts of helium, and traces of more complex atoms. Some of the atoms in this ejected matter experience forces that strip away the outer negative electric charge (electrons) and accelerate the positively charged nucleus to extremely high speeds. These highspeed atomic nuclei which drift around through interstellar space are called primary cosmic rays.
Earth is constantly bombarded from all directions with primary cosmic ray particles. These particles have sufficient energy to break up atoms which they encounter on reaching the upper levels of earth's atmosphere. The breakup of nitrogen and oxygen atoms by primary cosmic rays produces neutrons and atoms of carbon, boron, beryllium, helium, hydrogen, and possibly lithium. Neutrons are uniquely effective agents for producing atomic transmutation. The most frequent reaction produced by neutrons in air transmutes nitrogen into carbon which has 14 units of mass as compared with the 12 units characteristic of ordinary carbon (161/2 per cent heavier than an ordinary carbon atom), and is radioactive (that is, unstable). In the order of 22 pounds of radioactive carbon are produced per year in earth's upper atmosphere as a result of reactions produced by primary cosmic rays. This radioactive carbon is oxidized to carbon dioxide, which in turn is mixed throughout the atmosphere by air currents and utilized by plants along with nonradioactive carbon dioxide to form carbohydrates. The high solubility of carbon dioxide in water transfers a large portion of earth's radioactive carbon to the oceans. Radioactive carbon is distributed through all living material as a result of the dependence of animal life upon plant food.
Death of a plant or an animal terminates the processes by which its tissue structure receives carbon-14 from the environment. Since carbon-14 is unstable and spontaneously converts to nitrogen, the remains of once-living material will contain progressively smaller amounts of carbon-14 with the passage of time. Laboratory measurements on known amounts of radioactive carbon have established within an uncertainty of less than 100 years that in 5,730 years half of an initial amount of carbon-14 will disappear as a result of radioactive decay into nitrogen. On the basis of this information, 5,730-year-old remains of plants and animals may be expected to contain half as much radioactive carbon as they did at death.
Changes in the Carbon-14, Carbon-12 Ratio
For convenience, data on the radioactive carbon content of a sample is reported by specifying a radiocarbon age. The radiocarbon age describes the relative amount of radioactive carbon in the sample in terms of the relative amount of radioactive carbon in an oxalic acid standard supplied by the U.S. National Bureau of Standards. The NBS oxalic acid standard of carbon-14 activity is adjusted to provide a reference based on the average carbon-14 activity of wood which was growing in A.D. 1850. The strength in which the NBS standardized oxalic acid is supplied is such that 95 per cent of its specific radiocarbon activity is equivalent to the specific radiocarbon activ ity to be expected from wood growing in A.D. 1950 under conditions that prevailed in A.D. 1850. The radiocarbon age of a sample is the number of years that would be required for the specific radiocarbon activity level defined by the NBS oxalic acid standard to decay to the specific activity level measured in the sample.
Radiocarbon ages are based on a 5,568-year half-life for carbon-14 decay (the average of early less precise measurements), rather than on the more accurate value of 5,730 years in order to avoid confusion in comparing recent determinations with the large number of radiocarbon ages that appeared in the literature during the time when 5,568 years was the best available value for carbon-14 half-life. Since the radiocarbon time scale is arbitrary and does not directly measure real time, there is no need for basing it on an absolutely accurate determination of half-life. Those who are unhappy with the 5,568-year half-life convention can convert radiocarbon ages to a 5,730-year-based scale with a simple multiplication by 1.03. A sample with a specific radiocarbon activity equal to one-half 95 per cent of the specific radiocarbon activity of the NBS oxalic acid standard is assigned a radiocarbon age of 5,568. The radiocarbon date for the time when this sample ceased to exchange carbon with its environment would be 5,568 B.P., or 3618 B.C. (5,568A.D. 1950). In summary it may be said that radiocarbon ages are based on a 5,568-year half-life and are standardized against preindustrial-revolution conditions (A.D. 1850), and that A.D. 1950 is used for the zero point on the radiocarbon time scale. (Stuiver and Suess, Editorial Statement, Radiocarbon, vol. 8, 1966; Half-Life Statement, Proceedings of the Sixth International Conference on Radiocarbon and Tritium Dating.)
The reasons for basing radiocarbon ages on conditions in A.D. 1850 are of interest. Since A.D. 1850 man has introduced into earth's atmosphere large amounts of carbon dioxide produced by the use of fossil fuels—coal, oil, and natural gas. These fossil fuels contain a negligible amount of carbon-14 and are described as "infinite age" on the radiocarbon time scale. During the 100-year period between A.D. 1850 and A.D. 1950 use of fossil fuels released infinite age carbon equivalent to approximately 11 per cent of the total carbon presently contained in the atmosphere. Had this contribution of nonradioactive carbon been confined to the atmosphere it would have reduced the radiocarbon activity of the atmosphere by approximately 10 per cent. The actual decrease experienced (Suess effect) was only 1-5 per cent and probably averaged a strong 2 per cent, indicating that a large portion of the carbon released to the atmosphere by man's use of fossil fuels has been absorbed in the ocean (95 per cent of the carbon in earth's carbon dioxide exchange system is contained in the ocean). From A.D. 1950 to A.D. 1964, use of fossil fuels contributed carbon equivalent to approximately 6 per cent of the present atmospheric carbon content (Suess, 1955; Dyck, 1966).
Another factor related to human activity that influences the radiocarbon concentration in the atmosphere is the release of neutrons by atomic reactors and nuclear weapons. As a result of the Russian thermonuclear tests the relative amount of carbon-14 in earth's atmosphere approximately doubled between 1962 and 1965 (Thammeret and Thammeret, 1966; Berger and Libby, 1966). When thorough mixing of bomb products is achieved within the next five or six years the radiocarbon activity throughout earth's atmosphere is expected to possibly become three to four times greater than it was prior to 1962. Factors in the mixing of various components of earth's carbon dioxide exchange system which are not quantitatively understood may limit the atmospheric radiocarbon activity peak due to bomb products to little more than the doubling that has already been experienced (Libby, 1966-1; Fergusson, 1966).
By using as a "contemporary" reference the most recent radiocarbon activity level that has not been significantly affected by human activity, radiocarbon ages can more readily be used in studies of the past. The most accurate value for the "contemporary" activity level is considered to be 13.6 disintegrations per minute per gram of plant or animal carbon (Libby, 1966-1).
The Accuracy of Carbon-14 Dating
The measurements made in a radiocarbon laboratory do not determine historical ages or dates. The laboratory procedures only determine the amount of radioactive carbon that a sample contains at present. As described in the foregoing portion of this chapter, this amount of radioactivity is conveniently specified in terms of a radiocarbon age. The historical time lapse since a given specimen was a part of a living organism that exchanged carbon with its environment is an interpretation based in part on its radiocarbon age. The postulation of a date or age associated with the sample requires an assumption concerning the relative amount of radioactive carbon in the environment that supported the life of the organism from which the sample has been derived.
Reliable Only for 3,500-4,000 Years
Sagebrush sandals found in Fort Rock Cave in the southern part of central Oregon have a radiocarbon age of 9,300. If the relative percentage of radioactive carbon in earth's atmosphere during the growth of the sagebrush from which these sandals were made, was the same as it was in A.D. 1850, these sandals were made from sagebrush harvested 9,579 solar years ago.* There is no proof that these sandals were made 9,579 years ago, for radiocarbon ages can be reliably correlated with solar time only over the past 3,500 or possibly 4,000 years (approximately to the time of Moses) (Libby, 1966-11).
Major research effort is being directed toward developing reliable correlations between radiocarbon age and historical age. If the relative amount of radioactive carbon in the atmosphere had been at the A.D. 1850 level throughout the time life has existed on earth, radiocarbon ages, when adjusted to the 5,730-year half-life, would be identical with historical age. Tree-ring dating has established a precise and reliable chronology extending back to 59 B.C. By measuring the radiocarbon activity in precisely dated wood fiber, a chart can be prepared for converting radiocarbon age into historical age over the past 2,000 years (Stuiver and Suess, 1966). Such a chart (see Figure 1) shows fluctuations in the relative amount of carbon-14 in the atmosphere during this period, but these fluctuations appear to have been limited within a range of less than 5 per cent of the A.D. 1850 level. Because of the fluctuations in the atmospheric carbon-14 activity and the difficulties in standardizing one radiocarbon laboratory against another, the minimum uncertainty in any radiocarbon age is commonly considered to be plus or minus 100 years (see Radiocarbon, vol. 8, 1966, pp. -27, 213, 240, 340, and 453). Accordingly, if there are no contamination problems, the historical age of a sample which has a radiocarbon age no greater than about 2,000 years may confidently be considered to lie within a range of uncertainty equal to plus or minus twice the uncertainty specified for the radiocarbon age, providing this range is no less than plus or minus 200 years (see Radiocarbon, vol. 8, p. 256).
The foregoing statement must be qualified for samples that contain carbon derived from more than one period of history. A mud turtle from the Montezuma Well in Arizona which died in early A.D. 1961 was found to have an apparent radiocarbon age of approximately 15,000 years. This age is consistent with the radiocarbon age of the turtle's food supply which obtained most of its CO., from water rather than from atmosphere — artesian spring "fossil" water which had a radiocarbon age of 21,420 (Haynes, et al., 1966).
Attempts to derive historical age from radiocarbon age yield increasingly uncertain conjectures for samples older than 2,000 years. Tree-ring chronology has been extended from 59 B.c. to approximately 2400 B.C. using the bristlecone pine. The growth characteristics of this tree make it unsatisfactory for the establishment of a precise long-term growth-ring sequence. Attempts to correlate bristlecone pine growth rings with radiocarbon ages indicate that either ring counting has overestimated the age of the oldest bristlecone pine material by 500 to 1,000 years or the relative amount of carbon-14 in the atmosphere around 2000 B.C., was in the order of 10 per cent greater than in A.D. 1850 (Damon, et al., 1966).
It is a pleasure for the author to acknowledge indebtedness to Dr. Harold G. Coffin of the GeoScience Research Institute for the stimulus which led to the development of the foregoing material and also for the encouragement and assistance which he provided throughout all phases of the manuscript preparation