Radiocarbon dating, developed more than 60 years ago and awarded a Nobel Prize, was initially used to determine the age of archaeological and geological objects, but its scope soon expanded significantly. The method has proven its versatility and continues to be used with great success in science, technology, medicine and other areas of human activity.
The radiocarbon dating method has a significant impact on the development of various fields of science - from nuclear physics to criminology, but primarily geology and archaeology. In March 1949, an article was published that substantiated the operating principle of this method. Its authors - scientists from the University of Chicago (USA) Willard F. Libby, Ernst S. Anderson and James R. Arnold - showed that they can determine the age of geological or historical events, which took place not only hundreds and first thousands of years ago, but also up to 40-50 thousand years ago. Moreover, the proposed method had a fairly high accuracy and was completely independent of other technologies used at that time in the geosciences and archeology. It can be said without exaggeration that the radiocarbon method has made a genuine revolution in the concept of time in scientific knowledge. Recognition of the importance of this discovery was the award to W.F. Libby in 1960 Nobel Prize in chemistry.
This article gives brief information about the discovery and development of the method, its physical foundations; then follows a review of the application of the radiocarbon method in various fields of science and technology, its influence on the system of scientific knowledge of the 20th century. generally. There is extensive literature devoted to the radiocarbon method (see, for example:), therefore in the article the author refers only to the most general and comprehensive sources.
Immediately after the first works of W.F. Libby and his colleagues, the American Anthropological Association and the US Geological Society created a special commission to evaluate the first results radiocarbon dating, which in 1951 came to the conclusion that the data obtained were reliable and consistent with the existing scientific paradigm. The scientific community enthusiastically accepted the new research approach and began to actively use it in studying the past of the Earth and humanity; For many years, the method became the leading one in determining the age of certain objects. Since the mid-1950s, radiocarbon dating has spread throughout the world.
The new method also had opponents. Thus, archaeologists V. Milojcic and S. Yamanouchi believed that the radiocarbon dates of prehistoric monuments in Europe and Japan were too ancient, but the development of archaeological knowledge in these regions confirmed the correctness of the radiocarbon method. Simultaneously with the accumulation of factual material, that is, radiocarbon dates, there was a constant improvement of the methodological foundations laid by the founders of the method, and by the end of the 1970s, the basic provisions of the radiocarbon method were formulated, taking into account new data.
Basics of radiocarbon dating
In the natural environment of the Earth chemical element Carbon consists of three isotopes: two stable isotopes - 12 C and 13 C and one radioactive - 14 C, or radiocarbon. The 14 C isotope is constantly formed in the Earth’s stratosphere as a result of bombardment of nitrogen atoms by neutrons that are part of cosmic rays (Fig. 1, “formation” level). Over the course of several years, the “newborn” 14 C, along with the stable isotopes 12 C and 13 C, enters the Earth’s carbon cycle in the atmosphere, biosphere and hydrosphere (see Fig. 1, “distribution” level). While the organism is in a state of metabolism with its environment (for example, a tree receives carbon in the form of carbon dioxide from the atmosphere as a result of photosynthesis), the content of 14 C in it remains constant and is in equilibrium with the concentration of this isotope in the atmosphere. When an organism dies, the exchange of carbon with the external environment ceases; the content of the radioactive isotope begins to decrease, since there is no longer an influx of “fresh” 14 C from the outside (see Fig. 1, “decay” level). The radioactive decay of any element occurs at a constant rate, which is very precisely determined. Thus, for the 14 C isotope, the half-life is about 5730 years. Consequently, knowing the initial amount of 14 C in the body in relation to the stable isotopes 12 C and 13 C in a state of equilibrium (when the organism is alive) and the content of 14 C in fossil remains, it is possible to determine how much time has passed since the death of the carbon-containing substance. This is the essence of the model created by W.F. Libby et al. Despite the fact that in its development the radiocarbon method has gone through a number of significant updates, in the words of K. Renfrew - “revolutions”, its foundations, laid in 1949, remain unchanged to this day.
In other words, found in nature and in settlements ancient man the remains of plants and animals, as well as some other substances containing carbon, can be determined using the radiocarbon method to determine how much time has passed since the end of the life of the organism, that is, to establish the age of these objects. And this, in turn, means that it is possible to answer the age-old question of geologists and archaeologists: how long has this organism or ancient settlement existed? The radiocarbon method makes it possible to establish the age of carbon-containing substances up to 47,000 14 C years, which corresponds to an astronomical age of about 50,000 years.
It is known that the chemical element carbon is part of almost all living matter, as well as many nonliving substances (that is, created without the participation of living organisms). Thus, the radiocarbon dating method is truly universal. With its help, the age of a number of objects is determined, which can be divided into the following groups: “geological” - carbonate sediments of oceans and freshwater bodies, ice cores, meteorites; “biological” – wood and charcoal, seeds, fruits and twigs of plants, peat, soil humus, pollen grains, remains of insects and fish, bones, antlers, tusks, teeth, hair, skin and skin of vertebrates and humans, coprolites; “anthropogenic” - burnt bones, ceramics, flash metal, burnt food remains, traces of blood on ancient tools, fabrics, papyrus, parchment and paper. In some cases, for example, to study fluctuations in 14 C content depending on solar activity, its activity is measured in such “exotic” objects as wines, whiskey and cognacs.
Radiocarbon laboratories and their equipment
The first team to begin developing the radiocarbon method was the group of U.F. Libby in Chicago. Since the early 1950s, the number of laboratories in the USA, Canada, Europe and Japan has grown significantly, and at the end of the 1970s there were already more than 100 (Fig. 2: according to, with additions); there are currently about 140 of them on all continents. In total in the world in the second half of the 20th century. There were 250 installations for measuring 14 C content. At the end of the 1970s, the first laboratories using accelerator mass spectrometry (AMS) appeared; now there are already 40 of them. The list of radiocarbon laboratories is regularly updated and published in the main publication on this topic - the international journal Radiocarbon » (open access: www.radiocarbon.org).
The first radiocarbon laboratory in our country was organized in 1956 at the Radium Institute of the USSR Academy of Sciences and the Leningrad branch of the Institute of Archeology of the USSR Academy of Sciences (now the Institute of the History of Material Culture of the Russian Academy of Sciences); the inspirers of its creation were I.E. Old Man and S.I. Rudenko.
Currently, 7 laboratories actually operate in Russia: in Moscow - at the Geological Institute of the Russian Academy of Sciences, the Institute of Geography of the Russian Academy of Sciences, the Institute of Ecology and Evolution. A.N. Severtsov RAS; in St. Petersburg - at the Institute of the History of Material Culture of the Russian Academy of Sciences, St. Petersburg state university and VSEGEI; in Novosibirsk - at the Institute of Geology and Mineralogy of the SB RAS.
To carry out radiocarbon studies, complex instruments were required, the creation of which was the most important part of the development of the method. These include: a grid-wall Geiger-Muller counter with solid carbon as a carrier of 14 C (W.F. Libby, late 1940s); proportional gas meter (used since the 1950s); liquid scintillation counter - the most common type of device today (used since the 1960s); accelerator mass spectrometer.
UMS equipment is the most high-tech, complex and expensive. Despite this, the number of UMS laboratories in the world is constantly growing. Figure 3 shows the UMS installation at the University of Arizona with an operating voltage of 3 million eV. Briefly, the principle of its operation (Fig. 3, a) can be described as follows: negative ions carbon C? (including the 14 C isotope) obtained in the ion source (Fig. 3, b), are accelerated in the accelerator tank (Fig. 3, c) and are sent to measure their quantity in the detector (Fig. 3, d). After this, you can determine the number of 14 C atoms in the sample and, knowing their original number (measured for “modern” samples of various materials), determine the age of very small samples (down to 0.1 mg of carbon or less). This method has one undoubted advantage: to obtain a radiocarbon date, approximately 1000 times less carbon is needed than when using “traditional” liquid scintillation and proportional gas methods; in other respects (lower limit of sensitivity, requirements for sample selection, sample preparation, etc.) the UMS method differs little from them.
Application of the radiocarbon method
Archeology and Quaternary geology have been and remain the main areas of use of radiocarbon dating. In archaeology, the use of an independent method of determining age was truly revolutionary and significantly changed existing archaeological concepts. It is currently impossible to carry out serious archaeological work without the use of radiocarbon dating. Now, along with the analysis of “routine” objects, which include wood, charcoal and bones, age determination (mainly by the UMS method) of materials unsuitable in the recent past, such as individual seeds and fruits of plants, textiles, fatty acids ( lipids) in ancient ceramics and the ceramics themselves, blood remains on stone tools, rock paintings. The total number of radiocarbon dates for archaeological sites in the world today appears to be several hundred thousand; by the early 1960s there were no more than 2,400.
The results of using the radiocarbon method in the archeology of the Old and New Worlds are summarized in summary works. The most interesting and important examples include dating Shroud of Turin, Dead Sea manuscripts, rock paintings in caves in France and Spain, the world's oldest sites with ceramics and agriculture. The radiocarbon method has opened up wide possibilities for archaeologists and dendrochronologists, who can now “link” their data to an absolute time scale using the so-called “fluctuation comparison.” IN in this case fluctuations are sharp changes in the content of the 14 C isotope over the past 10–12 thousand years, which can be identified and compared with the peaks recorded on the internationally recognized curve.
The dating of ancient monuments was not without exposing forgeries. Even at the dawn of radiocarbon dating, one of the first samples, supposedly from Ancient Egypt, turned out to be a modern copy. A textbook example is the dating of the Piltdown “man” from England (the expected age is at least 75,000 years, the actual age is 500–600 years) and the remains of “Noah’s Ark” on Mount Ararat (their age was only 1200–1400 years, and not at least 5000 years according to biblical chronology) .
In Quaternary geology and paleogeography, the radiocarbon method is used as widely as in archaeology. With its help, the chronological parameters of the main warm and cold epochs over the last 40–50 thousand years have been established, especially for the last 10 thousand years (Holocene era) (see, for example:). The literature on the use of the radiocarbon method in geology is extremely extensive (see, for example:), so we will focus only on some examples: geochronology of the second half of the late Pleistocene of Siberia, dating of volcanic eruptions in Kamchatka; Ice Age chronology of northwestern European Russia and northern Eurasia as a whole.
Radiocarbon dating has become the most important tool in studying the process of extinction of large mammals (the so-called megafauna) at the end of the most recent geological period - the Pleistocene (from 2.6 million to 10 thousand years ago). Based on mass radiocarbon dating of the fossil remains of mammoths, woolly rhinoceroses and a number of other animal species, it was possible to establish the time and place of their final extinction. One of the most important achievements was determining the age of mammoth bones and tusks. O. Wrangel(North-Eastern Siberia): the remains turned out to be surprisingly “young” - from 9000 to 3700 years ago; today these are the latest mammoths on Earth. No less interesting are the results of radiocarbon dating of the bones of a fossil giant deer with antlers spanning up to 4 m: its last representatives lived in the Southern Urals and Trans-Urals until 6900 years ago. IN Lately Using direct UMS dating of Asian ostrich egg shells, evidence was obtained of its existence in East and Central Asia up to 8000 years ago.
The radiocarbon method is widely used in geophysics, oceanology, biology, medicine and many other sciences. Measurements of 14 C content in sea water have become firmly established in the practice of oceanological research (this makes it possible to identify patterns of circulation of the waters of the World Ocean) and in the study of groundwater on land and mineral springs. Dynamically developing direction can be called a study of the content of 14 C in objects such as meteorites and glaciers. The radiocarbon method helps in the study of astrophysical phenomena - fluctuations in solar activity, supernova explosions, etc.
Measurement of the activity of the 14 C isotope plays an important role in studies related to “technogenic” radiocarbon. As is known, in the second half of the 1950s, in connection with the start of testing hydrogen bombs“artificial” 14 C was formed in the atmosphere as a result of the emission large quantity free neutrons at the moment of a nuclear explosion (see Fig. 1, level “formation”), and the natural background was greatly disturbed. By 1965, the content of the 14 C isotope exceeded its “pre-bomb”, that is, background, amount by almost 2 times - 190% relative to the level of 1950 (Fig. 4) and even today has not yet returned to its original state. Now the activity of 14 C is about 105–110% of that in 1950, even the term “post-bomb 14 C” has appeared. However, every cloud has a silver lining: this phenomenon is widely used to determine the time of death of young (no older than 40–50 years) organisms; sometimes with the help of this approach it is possible to expose fakes of ancient human mummies. The phenomenon of artificial enrichment of the atmosphere with 14 C in the 1950s–1960s was the basis for many biomedical studies, where the 14 C isotope is a kind of “tag” (see, for example:). Pollution studies are carried out using 14C activity measurements natural environment radionuclides released during the production of fuel for the nuclear industry. And one can call it absolutely “exotic” use of radiocarbon dating in forensic science – to detect ivory trade(animals killed after 1955–1960 have a high “post-bomb” content of 14 C in their tusks) and drug smuggling (also based on the “post-bomb” effect). Truly, the scope of application of this method is almost limitless!
One of the areas of radiocarbon research, important for all sciences, in the 1960–2000s was the calibration of 14 C dates. The need for calibration is caused by the fact that the amount of the 14 C isotope in the atmosphere, hydrosphere and biosphere did not remain constant (as W.F. Libby and his colleagues initially believed), but changed under the influence of a number of external conditions, the main one of which was fluctuations in the recent geological past activity of cosmic rays producing radiocarbon (see Fig. 1). Therefore, the relationship between 14 C and calendar age is not linear. The influence of this factor, which complicates the conversion of radiocarbon ages to astronomical (calendar) dates, has now been overcome for the period of time from our days to 20,000 years ago; Work is successfully underway to draw up schedules for converting 14C dates into calendar dates up to the sensitivity limit of the radiocarbon method (about 45,000–50,000 14C years).
Prospects for the radiocarbon method
There are many examples of the influence of the 14 C-method on development scientific knowledge and revision of a number of provisions. Thus, it was on the basis of the results of 14 C dating of sections of Late Pleistocene and Holocene deposits that it was possible to build a reliable chronological basis for the history of climate and the natural environment of the Earth as a whole, which is extremely important when predicting climate changes in the future.
A striking illustration of the influence of radiocarbon dating on modern science and culture is to determine the age of one of the most famous Christian relics - the Shroud of Turin (which, according to legend, served as the burial shroud of Jesus Christ). It turned out to be about 690 14 C years, which corresponds to 1260–1390. AD . Obviously, in this case, the Shroud of Turin has nothing to do with the era of the life of Christ, which, according to biblical chronology, dates back to about 1–35 AD. AD Criticism of the conclusion about the “young age” of the shroud (with an attempt to refute it) was undertaken by the group of D.A. Kuznetsov, however, a detailed study of the processes they described did not find confirmation. Thus, the results of dating the Shroud of Turin can be considered scientifically reliable, and the need to confirm or clarify, using the radiocarbon method, the age of important objects of art, history and religion (paintings, engravings, manuscripts, shrouds, bones and relics of saints, etc.) has become after that obvious .
Another very significant example is the direct determination of the age of ancient people by 14 C dating of their bones. Work undertaken in this direction over the past 15–20 years with the remains of Neanderthals (Homo neanderthalensis) and modern humans (Homo sapiens sapiens) in Europe, North America and Asia has shown that in some cases the age of the bones is much “younger” than what was derived from archaeological or anthropological data. Nevertheless, for most objects the obtained 14 C dates are quite consistent with the expected results.
Openness and free access to information is one of the basic principles of the work of the community of specialists using the 14 C-method. Thus, interlaboratory verification of the radiocarbon age of specially selected samples is constantly carried out. Work is underway to improve the calibration procedure for 14 C-dates, which depends primarily on the degree of reliability of the source data. IN last years Results have been obtained that give hope that it will soon be possible to reliably calibrate 14 C dates back to 50,000 years ago.
In the near future, the most promising will be the use of small UMS installations, the operating requirements of which are not as stringent as for machines with an operating voltage of 3–6 million eV, and the capabilities of compact equipment are very large. The price of such small (operating voltage 200–500 thousand eV) devices is also an important factor; it is several times lower than the cost of large installations. Thus, the possibilities of directly dating very small or valuable objects are expanding - works of art, bones of Paleolithic people, etc., the list of objects is constantly growing. Thus, in recent years, the UMS method has been used to establish age of calcified bones from cremation burials; Such “burial fields” are common in Europe and Siberia. Priority areas also include the study of variations in the content of the 14 C isotope in the atmosphere up to 50,000 years ago based on the study of lake belt sediments (with annual layering). This, in particular, will make it possible to correlate natural and cultural events not only for the recent past of mankind, but also for the entire Late Paleolithic (up to 35,000–40,000 years ago). One of the most important aspects environmental protection - monitoring of radioactive contamination - is currently unthinkable without measuring the activity of the 14 C isotope in various natural and man-made objects.
The great scientific and practical potential of using the radiocarbon method will probably not be exhausted in the 21st century. Being one of the most universal and accurate methods for determining geological and archaeological age, as well as being a sensitive indicator of contamination of the natural environment with radioactive materials and other carbon-containing substances, the radiocarbon method is in demand today in various fields of fundamental science and applied research. This once again confirms the insight of U.F. Libby and his students - the founders of a new scientific direction.
First publication: Bulletin of the Russian Academy of Sciences, 2011, volume 81, no. 2, p. 127–133
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Currently, several methods are used to determine the age of archaeological finds, the most reliable of which is considered to be radiocarbon dating. However, even this most reliable method has huge errors. Thanks to the analysis of the data obtained, scientists realized that the rate of radioactive decay is not constant, as previously thought, since it is influenced by many external factors. This means that the “atomic clock” gets lost depending on external conditions.
Here are just some examples of dating with the “most accurate” method. Carbon-14 (14 C) dating showed that the newly killed seal died 1,300 years ago; the shells of living snails were 27,000 years old; the age of a shell of a living mollusk is 2,300 years old, etc. In the Belt cave (Iran), the underlying layer is dated to be approximately 6,000 years old, and the overlying one is 8,500 years old. That is, the reverse sequence of layers is obtained, which, of course, is impossible. And there are many similar examples.
How can we explain such a magnitude of error? exact method? The fact is that this analysis produced by determining the ratio of radioactive carbon-14 to stable carbon in a sample. It is believed that from the moment the vital activity of organic material ceases, “new” carbon-14 does not enter it, and the existing one gradually disintegrates at a constant rate, while stable carbon, of course, remains unchanged. However, under different conditions, carbon from the external environment (from everything nearby that contains carbon: volcanic phenomena, the action of fire and even high temperature, from the soil or from the atmosphere) can penetrate into the sample under study. And then the picture changes dramatically!
Rice. The principle of radiocarbon dating method
In addition, no one can know for sure how the level of carbon-14 in the atmosphere has changed over different periods. But scientists definitely know that it has changed, and significantly. Dendrological studies (analysis of tree rings) show that the level of carbon-14 in the earth's atmosphere has changed greatly over the past 4 - 5 thousand years (the oldest trees have this ring age; it is not possible to calculate the exact age, because annual rings change over time they simply merge, and in some cases several growth rings can form in one year). But no one knows what happened before; this is a matter of guesswork. Moreover, we cannot be sure that the carbon-14 in ancient tree rings corresponds to the carbon-14 in the atmosphere at the time the ring grew. Indeed, over the following years, this part of the tree was in direct contact with the adjacent layers of the trunk, with nutrients, sunlight, air and others external factors, which could not but affect the carbon content.
Thus, radiocarbon analysis can be trusted with great reserve and used only as one of the confirming factors of the age of the find, but not as the main and determining one.
In the works of critics of the radiocarbon method one can find the following quote: “Six reputable laboratories carried out 18 age analyzes on wood from Shelford in Cheshire. Estimates range from 26,000 to 60,000 years, with a range of 34,000 years.”1.
Also, many dates obtained using radiocarbon dating do not match the chronology established by historians and archaeologists based on documents and artifacts.
When discussing the radiocarbon dating method, one cannot help but pay attention to a few more points. Claims of significant age for ancient finds based on measurements of the amount of carbon-14 in them can be explained using the Bible. The fact is that before the flood, which, according to biblical calculations, occurred approximately 4.5 thousand years ago, the content of carbon-14 in the Earth's atmosphere should have been minimal. According to the Holy Scriptures, before the Flood, one of the layers of the atmosphere over our planet was a protective dome of water 2. The water shield protected the Earth from radioactive carbon-14 and harmful cosmic radiation. Therefore, as one would expect, in antediluvian samples the content of carbon-14 is extremely low, which is perceived by material scientists as a consequence of its decay, and therefore they talk about significant time periods.
In addition, carbon dating is not even theoretically designed to determine ages greater than 50,000 years. Scientists themselves openly declare this. Therefore, materialists cannot explain in any way why coal, oil and diamonds also contain carbon-14. After all, according to scientific data, carbon-14 has a short half-life (5,730 years) and simply cannot exist in samples dating back hundreds of thousands of years, let alone many millions, much less billions of years. However, carbon-14 is present in all layers, which confirms the young age of the Earth.
1 Hancock G. Traces of the Gods. M., 2006.
It is clear that in order to declare this or that artifact the property of some pre-civilization, it is necessary to establish its age by determining the exact date of creation of the object. However, modern archaeologists and historians are able to do this only in very rare cases. The vast majority of archaeological finds are dated approximately.
Radiocarbon dating method in archaeologists
Several methods are used to date found objects, but, unfortunately, each of them is not free from shortcomings, especially when applied to the search for traces of ancient cultures.
Radiocarbon method:
- - Formation of radiocarbon 14C
- - Decay of 14C
- - Condition of equilibrium for living organisms and disequilibrium for dead organisms, in which radiocarbon decays without replenishment from the outside
radiocarbon dating method
Currently, the most famous and frequently used is the radiocarbon method, which works with the radioactive carbon isotope C14. This method was developed in 1947 by the American physical chemist and Nobel Prize winner W.F. Libby. The essence of the method is that radioactive isotope C14 carbon is formed in the atmosphere under the influence of cosmic radiation. Together with ordinary carbon C12, it is found in the organic tissue of all living things. When an organism dies, the exchange of its carbon with the atmosphere stops, the amount of C14 decreases during decomposition and is not restored. Determination of the C14/C12 ratio in samples with known and constant speed decomposition of C14 (5568±30 years) and makes it possible to determine the age of the object, or, more precisely, the period that has passed since its death.
radiocarbon analysis laboratory
It would seem that everything is clear and simple, but with this method of dating samples, many dates turn out to be erroneous due to the contamination of objects or the unreliability of their connection with other archaeological finds. Therefore, long-term practice of using radiocarbon measurements has cast doubt on their accuracy. American archaeologist W. Bray and English historian D. Trump write: “Firstly, the dates obtained are never accurate, only in two out of three cases the correct date falls within this interval; Secondly, the decay rate of C14 is based on a half-life of 5568±30 years, and it is now clear that this half-life value is too low. It was decided not to change the value until a new one is adopted international norm; and, thirdly, the thesis about the invariability of the half-life rate of C14 also meets with objections.” Comparing the results of this method (from the same samples) with the results of dendrochronological analysis (that is, from tree rings), the already mentioned researchers conclude that radiocarbon dating can be trusted only for the last 2000 years.
Shroud of Turin photo, the most famous object for research using radiocarbon dating
Russian scientist F. Zavelsky says that the radiocarbon dating method depends on the validity of the assumptions accepted a priori in science:
- - assumption that the intensity of cosmic radiation falling on the Earth for tens of thousands of years has not changed;
- - radiocarbon in the earth’s atmosphere was irradiated with neutrons, “diluted” with stable carbon always in the same way;
- - the specific activity of carbon in the atmosphere does not depend on the longitude and latitude of the area and its height above sea level;
- - the content of radiocarbon in living organisms was the same as in the atmosphere throughout observable history. If one of the accepted assumptions turns out to be incorrect (or if several at once), then the results of the radiocarbon method may generally become illusory.
- Researcher A. Sklyarov writes about the use of radiocarbon analysis as follows: The “unobtrusive desire” of radiocarbon research laboratories to obtain in advance from historians and archaeologists the “approximate age of the sample” is generated by the carefully hidden error of the method itself and is of the nature of “the evil one”.
- Thus, for at least approximate dating, archaeologists have to simultaneously apply other methods, resorting to simple comparison results, based on which dating is best suited for a particular find or the entire archaeological complex. It is clear that the accuracy of dating in this case leaves much to be desired.
Shroud of Turin: positive and negative
The study of fragments of the Shroud of Turin is one of the most famous cases of using the radiocarbon method of dating an object of study.
Radiocarbon dating dated the shroud to the period of the 11th - 13th centuries. Skeptics consider this result to be confirmation that the shroud is a medieval fake. Supporters of the authenticity of the relic consider the data obtained to be the result of contamination of the shroud with carbon during a fire in the 16th century.
It is clear that in order to declare this or that artifact the property of some pre-civilization, it is necessary to establish its age by determining the exact date of creation of the object. However, modern archaeologists and historians are able to do this only in very rare cases. The vast majority of archaeological finds are dated approximately. Radiocarbon dating method in archaeologists Several methods are used to date found objects, but, unfortunately, each of them is not free from shortcomings, especially when applied to the search for traces of ancient cultures. Radiocarbon method: - Formation of radiocarbon 14C - Decay of 14C - Condition of equilibrium for living organisms and disequilibrium for dead organisms, in which radiocarbon decays without replenishment from outside radiocarbon...
Review
Radiocarbon dating has changed our understanding of the last 50,000 years. Professor Willard Libby first demonstrated it in 1949, for which he was later awarded the Nobel Prize.
Dating method
The essence of radiocarbon dating is to compare three different isotopes of carbon. Isotopes of a particular element have the same number of protons in the nucleus, but different number neutrons. This means that although they are very chemically similar, they have different masses.
The total mass of the isotope is indicated by a numerical index. While the lighter isotopes 12 C and 13 C are stable, the heaviest isotope 14 C (radiocarbon) is radioactive. Its core is so large that it is unstable.
Over time, 14 C, the basis of radiocarbon dating, decays into nitrogen 14 N. Most carbon-14 is created in the upper atmosphere, where neutrons produced by cosmic rays react with 14 N atoms.
It is then oxidized into 14 CO 2, enters the atmosphere and mixes with 12 CO 2 and 13 CO 2. Carbon dioxide used by plants during photosynthesis and from there passes through the food chain. Therefore, every plant and animal in this chain (including humans) will have an equal amount of 14 C compared to the 12 C in the atmosphere (14 C: 12 C ratio).
Limitations of the method
When living things die, tissue is no longer replaced and radioactive decay of 14 C becomes apparent. After 55 thousand years, 14 C decays so much that its residues can no longer be measured.
What is radiocarbon dating? can be used as a "clock" since it is independent of physical (eg temperature) and chemical (eg water content) conditions. In 5730 years, half of the 14 C contained in the sample decays.
Therefore, if the ratio of 14 C: 12 C at the time of death and the ratio today are known, then it is possible to calculate how much time has passed. Unfortunately, identifying them is not so easy.
Radiocarbon dating: uncertainty
The amount of 14 C in the atmosphere, and therefore in plants and animals, was not always constant. For example, it varies depending on how many cosmic rays reach the Earth. This depends on solar activity and the magnetic field of our planet.
Fortunately, it is possible to measure these variations in samples dated by other methods. It is possible to calculate tree rings and changes in their radiocarbon content. From this data a "calibration curve" can be constructed.
Currently, work is underway to expand and improve it. In 2008, only radiocarbon dates up to 26,000 years could be calibrated. Today the curve has been extended to 50,000 years.
What can be measured?
Not all materials can be dated using this method. Most, if not all, organic compounds allow radiocarbon dating. Some inorganic substances, such as the aragonite component of the shells, can also be dated because carbon-14 was used in the formation of the mineral.
Materials that have been dated since the method's inception include wood, twigs, seeds, bones, shells, leather, peat, silt, soil, hair, pottery, pollen, wall paintings, coral, blood remains, textiles, paper, parchment, resins and water.
Radiocarbon dating is impossible unless it contains carbon-14. The exception is iron products, in the manufacture of which coal is used.
Double count
Because of this complication, radiocarbon dates are presented in two ways. Uncalibrated measurements are reported in number of years prior to 1950 (BP). Calibrated dates are also presented as BC. BC, and after, and also using the calBP unit (calibrated up to the present, until 1950). This is the "best estimate" of the actual age of the sample, but it is necessary to be able to go back to old data and calibrate it as new research continually updates the calibration curve.
Quantity and quality
The second difficulty is the extremely low prevalence of 14 C. Only 0.0000000001% carbon in modern atmosphere represents 14 C, which causes incredible difficulties for measurements and makes it extremely sensitive to contamination.
In the early years, radiocarbon dating of decay products required huge samples (for example, half femur person). Many laboratories now use an accelerator mass spectrometer (AMS), which can detect and measure the presence of various isotopes, as well as count the number of individual carbon-14 atoms.
This method requires less than 1 g bone tissue, but few countries can afford more than one or two AMS, which cost more than $500 thousand. For example, Australia has only 2 such instruments that are capable of radiocarbon dating, and they are unattainable for much of the developing world.
Cleanliness is the key to precision
In addition, the samples must be thoroughly cleaned of carbon contaminants from the adhesive and soil. This is especially important for very old materials. If 1% of an element in a 50,000-year-old sample comes from a modern contaminant, it will be dated as 40,000 years old.
For this reason, researchers are constantly developing new methods effective cleaning materials. They can have a significant impact on the result given by radiocarbon dating. The accuracy of the method has increased significantly with the development of a new cleaning method activated carbon ABOx-SC. This made it possible, for example, to delay the date of the arrival of the first people in Australia by more than 10 thousand years.
Radiocarbon dating: criticism
The method proving that much more than the 10 thousand years mentioned in the Bible has passed since the origin of the Earth has been repeatedly criticized by creationists. For example, they argue that after 50,000 years there should be no carbon-14 left in the samples, but coal, oil and natural gas, believed to be millions of years old, contain measurable amounts of this isotope, which is confirmed by carbon dating. at the same time there is more background radiation, which cannot be eliminated in the laboratory. That is, a sample that does not contain a single atom of radioactive carbon will show a date of 50 thousand years. However, this fact does not cast doubt on the dating of the objects, and certainly does not indicate that oil, coal and natural gas are younger than this age.
Creationists also note some oddities in radiocarbon dating. For example, the dating of freshwater mollusks determined their age to be greater than 2000 years, which, in their opinion, discredits this method. In fact, it has been established that shellfish receive most carbon from limestone and humus, the 14 C content of which is very low, since these minerals are very old and do not have access to air carbon. The radiocarbon dating, the accuracy of which in this case can be questioned, is otherwise consistent with reality. Wood, for example, does not have such a problem, since plants receive carbon directly from the air, which contains a full dose of 14 C.
Another argument against the method is the fact that trees are capable of forming more than one ring in one year. This is true, but more often it happens that they do not form growth rings at all. The bristlecone pine, which is the basis for most measurements, has 5% fewer rings than its actual age.
Setting the date
Radiocarbon dating is not only a method, but also exciting discoveries about our past and present. The method allowed archaeologists to arrange finds in chronological order without the need for written records or coins.
In the 19th and early 20th centuries, incredibly patient and careful archaeologists linked pottery and stone tools from different geographic areas by looking for similarities in shape and pattern. Then, using the idea that object styles evolved and became more complex over time, they could place them in order.
Thus, large domed tombs (known as tholos) in Greece were considered to be the predecessors of similar structures on the Scottish island of Maeshowe. This supported the idea that the classical civilizations of Greece and Rome were at the center of all innovation.
However, radiocarbon dating revealed that the Scottish tombs were thousands of years older than the Greek ones. The northern barbarians were capable of designing complex structures similar to the classical ones.
Other notable projects included assigning the Shroud of Turin to the medieval period, dating the Dead Sea Scrolls to the time of Christ, and the somewhat controversial periodization of the paintings at 38,000 calBP (about 32,000 BP), thousands of years earlier than expected.
Radiocarbon dating has also been used to determine the timing of the extinction of mammoths and has contributed to the debate over whether modern people and Neanderthals or not.
The 14 C isotope is used not only to determine age. Radiocarbon dating allows us to study ocean circulation and trace the movement of drugs throughout the body, but this is a topic for another article.
The researchers measured the carbon-14 content of trees growing in southern Jordan, determined their age and compared the resulting dates with the standard method scale. As a result, they found discrepancies of an average of 19 years. A relatively minor inaccuracy can nevertheless have a significant impact on early biblical archaeological research and paleoecological reconstructions. The results are presented in the journal Proceedings of the National Academy of Sciences.
Radiocarbon dating is one of the main methods for dating plants and archaeological objects containing organic material. Scientists have been using it for a long time, so standard scales have now been developed for the Northern and Southern Hemispheres, which are called calibration curves. They represent the dependence of calendar and radiocarbon ages. These curves are fairly close to a straight line, but reflect variations in isotope ratios at different times.
“We have begun to test the assumptions on which the entire field of radiocarbon dating rests,” says lead author Stuart Manning from Cornell University in the US. - From atmospheric measurements of the last 50 years, we know that the content of carbon isotopes varies throughout the year, and we also understand that in various points In the northern hemisphere, plants often grow actively in different time. "We wanted to find out how much the [accuracy of radiocarbon dating] varies depending on the [geographic] area being studied, and whether this might affect archaeological dating."
The material for the study was trees growing in the south of Jordan, the age of which is known to scientists. The authors measured the age of their tree rings using radiocarbon dating and found a shift of 19 years relative to the standard Northern Hemisphere calibration curve. As a result, scientists say, many works on the history of this region, which also includes modern territory Israel may be based on incorrect assumptions. For example, it makes sense to double-check the dating of early biblical events, since the calibration curves used in many studies are simply not suitable for this area.
The authors applied the results to several previously published chronological tables and found out that even a small shift in dating can lead to a change in calendar dates, which must be taken into account when deciding controversial issues history, archeology and climate of the past. “Our work should be the beginning of a reexamination and rethinking of the timeline of archeology and early history of the southern Levant during the early biblical period,” Manning concludes.
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