Are Geological and Archeological Carbon Dating Methods Reliable?
Submitted by on Mon, 26/01/2015 - 09:38
Dear Brother / Sister,
Both radioactive methods and other methods used in determining the age of geological and archeological materials are not exact since they are based on some assumptions and estimations. Therefore, there are hesitations whether the ages determined by these methods are real ages.
In geology, "age" (date) has a relative meaning. One of the two rock masses that are side by side or one over the other is younger or older than the other. If there was not a transformation, the rock under the other is older. It was first expressed by Nicolas Steno in 1669.
Various methods are used in order to determine the age of the geological and archeological materials. They are as follows:
1. Geological Dating
In this method, comparison is essential. For instance, if the carboniferous land in a region resembles the land in another region in terms of rocks, fossils and morphological structure, it is decided that the land in the second region has the same carboniferous age.
2. Paleontological Dating
In this method, the age of the rock is determined based on the types of fossils the rock includes. During the excavations made by William Smith in England in 1770, he determined that the fossils he observed in the layers had not been placed randomly but based on a certain order and that the same types of fossil organisms existed in the same group of layers and different types of fossil organisms existed in different layers; thus, he concluded that layers of rock containing the same fossils had the same age. The studies he did afterwards confirmed this thought of his. 2
In geological eras, there are fossils which existed for short spans of time and vanished. They are called “Characteristic or key fossils” or “Layer-determining fossils”. Layer-determining fossils are like calendars and they are of significance importance in determining the geological age of the sediment they are located in. For instance, Trilobites, which emerged suddenly at the beginning of the Paleozoic Era, spread to a large area in a very short time and suddenly disappeared at the end of the Paleozoic Era. Therefore, the age of sediment in which Trilobites exit is Paleozoic. Similarly, Ammonites indicate the Mesozoic, Nummulites the Tertiary and mammals the Quaternary.
Judging by characteristic fossils which lived in different ages and eras, “geological columns” which display the age of each era and layer-determining fossils it includes have been formed. With the help of a characteristic fossil which might be found in an area, the age of that area is determined by looking up this geological column.
Criticism of the Method of Paleontological Dating
The age of rocks is determined by the index fossils they contain However, how can it be determined which index fossil shows which age? The answer is “evolution”. That is, since it is claimed that evolution exists in the same direction on the earth, phases of evolution of an organism that lived in a certain era must provide an infallible criterion in order to define sediments stored in this era. This is the basic principle of the evolution theory
Morris states that the only way to classify rocks in chronological order is fossils. The criterion that is necessary to move fossils to the very special place in this chronology is the claim that “life evolves from the simple to the complex”. Evolution of living organisms, though, is based upon fossil records. Evidence for the existence of evolution is fossils. Fossils are ranged in chronological order according to the evolution theory. Thus, this matter has become a strong reasoning system as a vicious circle.1
Dunbar states the following regarding the issue:
“Fossils provide the only evidence based on historical data that life evolves from the simple to the complex.” 3
3. Varve Dating
Water deposits the materials it carries in low areas. The age of a sedimentary sequence can be determined through this speed of sedimentation. The waters that form especially from melting glaciers deposit in lakes or low areas. The rate of melting is slow in winter and these waters cause the formation of thin layer since they carry materials with fine grains. In summer, the rate of melting is fast and they form a thick layer by carrying materials with large grains. Thus, one thin layer and one thick layer form every year. It is possible to determine the age by counting these rings like the rings of a tree. The first dating by making use of the varves of the layered rocks was made by the Swedish scientist De Geer in 1905 for the first time. In Swedish, "varve" means "periodic repetition".
Acting upon the rate of depositing, it was shown that the River Nile deposited sediment of 30 cm thick every 400-500 years for 3000 years. It is claimed that geological dating is possible through determining the amount of salt in the oceans. It is taken into account that the salts there are carried out in a certain time from the rocks around. Calculating the rate between the amount of sodium ions in the ocean waters and the amount of sodium reaching the sea from the land through rivers, Joly found that the amount of Na+ contained in the ocean to be to 15.627 x 1012 tons and the amount of Na+ entering the oceans to be 15.727 x 104 tons. Acting upon this, he calculated the age of the oceans as 99.4 million years. This method is criticized in that this number is very small and that the rate of Na+ constantly changes.
Criticism of Varve Method
The precipitation regime and the structure of the soil play an important part in Varve method. The climate changes to be seen among seasons and years will affect the texture and structure of the material to be carried by the same amount of water. Floods seem to be a disadvantage in the formation of the varve. For, more sediment will be carried and deposited by flood water compared to the material carried by normal water. This will substantially affect the result of the Varve method, which bases its calculation for determining the age on the sediment that is deposited.
4. Age Determination by Means of Radioactive Elements
Becquerel determined for the first in 1896 that some invisible rays emanated from uranium salts. Madam Curie determined in time 1897 that thorium also emitted rays and called this event “radioactivity”. Radioactive elements emit alpha, beta and gamma rays. These rays are identified through devices like Geiger counter and centilometer thanks to the radiation effect they exert on the photograph film.
It is possible to divide age determination by meansof radioactive elements into two based on the direct and indirect effects of radioactive e elements.
4.1. Methods Based on the Indirect Effects of Radioactivity
4.1.1. Uranium Method
Uranium Method is a group of age determination methods. All of these methods depend on the principle of generation of lead and helium from uranium and its fellow element, thorium, in their long chains of decay. This event is called alpha degradation. In this event, alpha particles separate from the nuclei of main atoms at a constant speed. They are positively charged atoms of helium gas.
The most important radioactive elements are uranium and thorium. Uranium has two isotopes. The first one is U238, whose half life is 4,5 billion of years. The other one is U235, whose half life of is 0,7 billion of years.
The half life of Thorium (Th232) is 14,1 billion of years. By giving off definite proportions of Helium atom, they generate lead isotopes as shown in the diagram:
U 238 ----> Pb 206 + 8 He 4
U 235 ----> Pb 207 + 7 He 4
Th 232 ----> Pb 208 +6 He 4
Three isotopes of lead exist in galenite (PbS, which is a normal lead mineral. It is possible to find Pb204, which is another isotope of lead, in any layer that contains these elements. That is why, it is called "common lead". Although the amount of the other isotopes always increased throughput geologic eras, the amount of Pb204 always remained the same. Therefore, the importance of Pb204 in finding radiometric age is great. In a mineral that contain lead, when the amount of Pb204 is subtracted from the general amount of lead, the Pb isotopes that are the outcome of radioactive degradation remain. When their amounts are determined, the age of the mineral they are located in is found.
In radioactive elements, the number of atoms occurring through degradation (n) is directly proportional to the atom number of the radioactive elements (N).
This law is represented as follows in mathematics:
n = N.e-λt
n = the number of atoms remaining after a certain time (“t”)
N =the number of atoms that were present at the beginning of time; that is, when t=0.
l = Radioactive degradation constant (it is characteristic for each element).
If the amount of the radioactive elements present at the beginning and the amount of the element that formed up to now as a result of radioactivity are known, the time necessary for the formation of the last amount can be calculated.
Degradation speed is not dependent on time and the age of radioactive isotopes. It is not possible to determine this speed statistically. For instance, out of 10 million radium atoms (N), 4273 (n) of them undergo degradation every year. The rate of n/N is called "degradation constant".
This value for radium is
l = n / N = 4273 / 107
l = 0.0004273 per year.
Half life is:
T= 0.693 / l
T = 0.693 / 0.0004273 = 1622 years.
Criticism of Uranium Method
There are some objectionable parts in the methods of age determination depending on radioactive decay of uranium. They might be summarized as follows:
1. Uranium minerals are always found in open systems.
Since the layer consisting uranium is not in a closed system, it is exposed to external effects. For instance, uranium can easily resolve in ground water. Radon gas, an intermediate element, may easily pass inside or outside the uranium system. Henry Fauld, an expert on radioactive age determination, points out to the following regarding the issue:
“In geological time, both uranium and lead translocated in shale. Detailed analysis showed appropriate ages have not been determined with these elements. Similar drawbacks are encountered in attempts of age determination of mineral ores which consist uranium and radium. It is known that different ages are found on samples taken from the same points and plenty of chemical activities took place.” 4.
2. The disintegration rate of uranium might be changeable.
Since radioactive degradation is controlled by atomic structure, it is not easily affected by other events. Nevertheless, factors which are able to affect atomic structures might also influence radioactive disintegration rate. The most outstanding example to this is cosmic radiation and neutrinos. Another example is free neutrinos which come out of reactors or which are generated out of various reasons. If anything which might increase the amount of these particles on the earth is to come into existence, it is sure to accelerate radioactive disintegration rates.
3. Daughter elements might have been present therein where the layer began to form. It is possible that radiogenic daughter elements which are generated by the disintegration of uranium and thorium might have been already present when these minerals began to form. It has been found today that rocks which were produced by lava flowing through the internal layers of the earth consist of both radiogenic and combined lead.
4. All of the daughter elements might not be peculiar to that layer. All of the daughter elements which were produced by radioactive disintegration may not remain in the same layer; other daughter elements which were produced in a different layer might have moved there.
4.1.2. Potasyum-Argon Method
Potassium minerals exist in most of the volcanic rocks and some sediments. They have a wide range of usage. Potassium 40 transforms into Argon 40 by catching electrons with a speed of 1,3 billion years half life.
4.1.3. Rubidium-Strontium Method
This method is based on the transformation of Rubidium 87 into Strontium 87 with 47 billion years half life. The half life of Rubidium is regarded as 60 billion years by some authorities and 120 years by others. This method needs to be arranged based on uranium method. Therefore, it is not more reliable than uranium age determination method. In terms of application and the drawbacks in application, Potassium-Argon Method and Rubidium-Strontium Method, and the other radioactive methods are similar to uranium method.
4.1.4- Radiocarbon (C14) Method
Radiocarbon is the name given to the unstable isotope Carbon fourteen (C14). Carbon twelve (C12) is called “natural carbon” and it is not radioactive. Radiocarbon is produced from the reactions among nitrogen-fourteen (N14) in the atmosphere, due to cosmic radiation in superior layer of atmosphere. Carbon-12 consists of six protons, six neutrons and six orbital electrons. Carbon-14, though, includes eight neutrons in the nucleus. These two extra neutrons make the atom unstable. One of these neutrons gives off a beta particle, producing a new nucleus which consists of seven protons and seven neutrons is produced. This new structure is the Nitrogen-14. Thus, the unstable Carbon-14 turns into the stable Nitrogen-14. Its half life is 5730 years
Carbon-14, which is generated in the atmosphere, is immediately oxidized as CO2 and spreads to the air, water and to living organisms. Normally the ratio of radioactive carbon dioxide and non-radioactive carbon dioxide (C14/C12) in the air is fixed and it is accepted that 100 years should pass so that this fixed rate can be reached.
The ratio of C14/C12 in living organisms should be fixed as well. The equality of this ratio does not change as long as the organism is alive. However, when the organism dies, the ratio of C14 to C12 decreases gradually since the organism cannot take CO2 in from the air any longer. When this decreasing ratio strikes ½, the length of time from the death of that organism must be 5730 years because the half life of C14 is 5730 years. In five half lives, in other words, in around 29 thousand years, only 1/32 of the original amount of radiocarbon is to be emitted. Radiocarbon method can only be used to determine the ages around 80 thousand years at most. For older materials, uranium method is applied.
Criticism of Radiocarbon method
Radiocarbon method is criticized because it is based on some assumptions. Here are the opposed points:
1. A number of living systems do not have the standard ratio of C14/C12. Carbon-14 method is based on the theory which claims that when all living organisms die, they include a standard ratio of C14/C12 . Nevertheless, many samples did not display this ratio. For example, with this method, age of living mollusks was determined to be 2300 years old. Such ratio shows that the environment the organism is in includes higher amount of C14 than expected and therefore, there is an exchange of carbon between the organism and the environment. 5
2. Radiocarbon might not decrease at a stable rate in each organism.
Radiocarbon disintegration is influenced by environmental radioactivity, especially free neutrons and cosmic radiation and their disintegration rates change as a result.
3. The rate of natural carbon might have been different in the past.
In the past, the vegetation was either more or less than it is now. The ratio of C14/C12, therefore, is to be higher or lower. For this reason, the radiocarbon age of the materials of these periods is to be measured older or younger than the true age. This matter is the same for the amount of carbon dioxide in the atmosphere. If volcanoes had emitted carbon dioxide in the past, in this case, the amount of carbon dioxide at that time should be different than it is now.
4. The rate of radiocarbon might not have reached a stable condition. It is assumed that the ratio of C14/C12 reaches a stable condition in a certain length of time. In other words, the amount of C14 in the atmosphere is equal to the amount of C14 disintegrated on the earth. For this reason, the incoming and outgoing amount of C14 needs to be equal. However, there are some things which prove that this is not always in this way. In the same way, it is stated that the measurable amount of radiocarbon generated in a year on the earth is 25% more than the amount of disintegrated radiocarbon. 5-8
4.2. Methods Based on the Indirect Effects of Radioactivity
The indirect effects of radioactivity occur with the rays of radioactive breakdowns. These rays affect the rock as if they bombard the rock. The source of the rays might be the natural radioactive minerals especially in the rock or the alpha or cosmic rays of the heavy metals around and their fission.
4.2.1. Pleochroic Halos Method
Pleochroic halos occur around small inclusions of radioactive minerals, such as zircon, and monazite, especially in biotites. If inclusions are tiny,pleochroic halos are in the shape of full spheres and they resemble a circle in thin section. The diameters of concentric spheres have constant values; the diameter of each sphere is equal to the distance covered by alpha ray. The relation between the light transmittance ofpleochroic halos and the alpha ray it gets with its effect is determined by experiments; therefore, it can be used in age determination.
This method is criticized in various ways. The experiments that are carried out show that the light transmittance in pleochroic halos obtained artificially change periodically and that it is affected especially by increase in heat.
4.2.2. Trace Method
This method is based on the count of the traces of rays emitted when a mineral breaks down due to radioactivity.
4.2.3. Metamictization Method
This method is based on the irregularity that can be determined by measuring through X rays of crystal networks in a mineral.
4.2.4. Thermoluminescence Method
Some electrons connected to the crystal inner structure affected by rays are released and then entrapped in the faulty places of the crystal network. All of the electrons in that state form a dynamic system with a higher level of energy than that of their normal place. Electrons return to their normal places with the effect of heat when energy comes out in the form of light; thus, the energy level of the mineral affected by radioactivity can be found.
These methods, which are based on the indirect effect of radioactivity, are still in the phase of development and their range of usage is narrower than the previous ones.
5. A general assessment on geological and archaeological dating methods
Both radioactive method and other methods applied in geological and archaeological dating are not at the expected sensitivity since they are based on several assumptions and predictions. For this reason, some doubts arise on the correctness of ages determined. However, as there are similar errors in age-determination of every material, findings are important in terms of being approximate ages rather than exact ages. For example, material A, which is found to be at 150 million years of age, is three times older than material B, which is found to be 50 million years old. That is to say, if material B is 5 thousand years old indeed, then, the material A should be at 15 thousand years old.
There are no other alternatives for the methods mentioned above.
1. Morris, H. and Parker,G.E. What is Creation Science? Master Book Publishers. California. 1982. Translated by Â.Tatlı, Keha, E., Marangoz, C., Solak, K. ve Hasenekoğlu, İ. Yaratılış Modeli. Millî E. Bakanlığı Basımevi. Ankara. 1985.
2. Ketin, I. Genel Jeoloji. Cilt 1. İTÜ Yayını. 1982, issue 1096.
3. Dunbar, C.O. Historical Geology. New York. John Wiley Sons. Inc. 1949, p.52.
4. Fault, H. Age of Rocks, Planets and Stars. New York. McGraw-Hill Book. Co. Inc. 1966, p.61.
5. Keith, M.S. and Anderson, G.M. Radiocarbon Dating: Fictitious Results with Mollusc Shells. Science, August, 16. A. 634, 1963.
6. Libby, W.F. Radiocarbon Dating. University of Chicago Press.1955, p.7.
7. Lingelfelter, R. E. Production of C-14 by Cosmic & Ray Neutrons. Reviews of Geographics. 1963, Vol. 1. p.51.
8. Suess, H.E. Secular Variations in the Cosmic Ray Produced Carbon-14 in the Atmosphere and their Interpretations. Journal of Geophysical Research. 1965, Vol.7. p.594.
Prof. Dr. Adem Tatlı
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