Radiocarbon analysis has changed our view of the past 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 analysis is to compare three different carbon isotopes. Isotopes of a particular element have the same number of protons in the nucleus, but different numbers of neutrons. This means that with great chemical similarity 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 analysis, decomposes into 14 N nitrogen. Most of the carbon-14 is created in the upper atmosphere, where neutrons that form under the influence of cosmic rays react with 14 N atoms.
It then oxidizes to 14 CO 2 , enters the atmosphere and mixes with 12 CO 2 and 13 CO 2 . Carbon dioxide is used by plants in the process of 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 12 ° C in the atmosphere (ratio of 14 ° C: 12 ° C).
Method Limitations
When living things die, the tissue is no longer replaced, and the 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 analysis? Radioactive decay can be used as a “clock”, since it does not depend on physical (eg, temperature) and chemical (eg, water content) conditions. Over 5730 years, half of the 14 C contained in the sample disintegrates.
Therefore, if you know the ratio of 14 C: 12 C at the time of death and today's ratio, then you can calculate how much time has passed. Unfortunately, defining them is not so simple.
Radiocarbon Analysis: Accuracy
The amount of 14 C in the atmosphere, therefore, in plants and animals, was not always constant. For example, it varies depending on how many cosmic rays reach the Earth. It depends on the solar activity and the magnetic field of our planet.
Fortunately, these fluctuations can be measured in samples dated by other methods. You can calculate the annual rings of trees and the change in their content of radiocarbon. 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 expanded to 50,000 years.
What can be measured?
Not all materials can be dated by this method. Most, if not all, organic compounds allow for radiocarbon analysis. Some inorganic substances, such as the aragonite component of shells, can also be dated, since carbon-14 was used to form the mineral.
Materials that have been dated since the creation of the method include charcoal, wood, twigs, seeds, bones, shells, skin, peat, silt, soil, hair, ceramics, pollen, wall paintings, corals, blood residues, fabrics, paper, parchment, resin and water.
Radiocarbon analysis of the metal is not possible if it does not contain 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. Non-calibrated measurements are given by the number of years before 1950 (BP). Calibrated dates are also presented as BC. e., and after, as well as using the calBP unit (calibrated to date, until 1950). This is the “best estimate” of the actual age of the sample, but it is necessary to be able to revert to the old data and calibrate them, as new studies are constantly updating the calibration curve.
Quantity and quality
The second difficulty is the extremely low prevalence of 14 C. Only 0.0000000001% of the carbon in the modern atmosphere is 14 C, which causes incredible difficulties for measurements and makes it extremely sensitive to pollution.
In the early years, radiocarbon analysis of decay products required huge specimens (for example, half of the human femur). 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 of bone tissue, but only a few countries can afford more than one or two AMS, the cost of which exceeds $ 500 thousand. For example, Australia has only 2 such instruments that are capable of radiocarbon analysis, and they are unattainable for most of the developing world.
Cleanliness is the key to accuracy
In addition, samples should be thoroughly cleaned of carbon contaminants from glue and soil. This is especially important for very old materials. If 1% of an element in a sample aged 50 thousand years comes from a modern pollutant, it will be dated as forty thousand years old.
For this reason, researchers are constantly developing new methods for the efficient cleaning of materials. They can have a significant impact on the result that radiocarbon analysis provides. The accuracy of the method increased significantly with the development of a new ABOx-SC activated carbon purification method. This allowed, for example, to postpone the date of arrival of the first people in Australia by more than 10 thousand years.
Radiocarbon Analysis: Criticism
The method, proving that much more than 10 thousand years, mentioned in the Bible, has passed from the moment of the Earth’s origin, has been criticized by creationists several times. For example, they argue that for 50 thousand years carbon-14 should not remain in the samples, but measurable amounts of this isotope are contained in coal, oil, and natural gas, which are supposedly millions of years old, which confirms the radiocarbon analysis. The measurement error in this case is more than background radiation, which is impossible to get rid of 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 facilities, and moreover, does not indicate that oil, coal and natural gas are younger than this age.
Creationists also note some oddities of radiocarbon analysis. For example, dating of freshwater mollusks identified their age as exceeding 2000 years, which, in their opinion, discredits this method. In fact, it has been established that mollusks receive most of the carbon from limestone and humus, the content of 14 C in which is very low, since these minerals are very old and do not have access to air carbon. Radiocarbon analysis, the accuracy of which in this case can be questioned, is otherwise true. Wood, for example, does not have such a problem, because 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 able to form more than one ring in one year. This is true, but more often it happens that they do not form annual rings at all. The spinous pine, on the basis of which the majority of measurements were carried out, has 5% less rings than its actual age.
Date setting
Radiocarbon analysis is not only a method, but also an exciting discovery in our past and present. The method allowed archaeologists to arrange the finds in chronological order without the need for written records or coins.
In the 19th and early 20th centuries, incredibly patient and cautious archaeologists linked ceramics and stone tools of different geographical areas by looking for similarities in shape and patterns. Then, using the idea that the styles of objects evolved and became more complex over time, they could place them in order.
Thus, the large domed tombs (known as tolos) in Greece were considered the forerunners of such structures on the Scottish island of Meishau. This supported the idea that the classical civilizations of Greece and Rome were at the center of all innovation.
However, as a result of radiocarbon analyzes, it turned out that the Scottish tombs were thousands of years older than the Greek. Northern barbarians were able to design complex structures similar to the classical ones.
Other notable projects included the assignment of the Shroud of Turin to the medieval period, the dating of the Dead Sea scrolls to the time of Christ, and the somewhat controversial periodization of drawings in the Chauvet cave with an age of 38,000 calBP (about 32,000 BP), thousands of years earlier than expected.
Radiocarbon analysis was also used to determine the time of the extinction of mammoths and contributed to the debate about whether modern people and Neanderthals met or not.
The 14 C isotope is used not only to determine age. The method of radiocarbon analysis allows you to explore the circulation of the ocean and to trace the movement of drugs throughout the body, but this is the topic of another article.