Radiocarbon analysis 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 analysis is to compare three different isotopes of carbon. Isotopes of a particular element have the same number of protons in the nucleus, but a different number of neutrons. This means that despite their great chemical similarity, they have different masses.
The total mass of an isotope is indicated by a numerical index. While the lighter isotopes 12C and 13C are stable, the heaviest isotope 14C (radiocarbon) is radioactive. Its core is so large that it is unstable.
Over time, 14C, the basis of radiocarbon dating, decays into nitrogen 14N. Most carbon-14 is created in the upper atmosphere, where neutrons produced by cosmic rays react with atoms 14N.
Then it oxidizes to 14CO2, enters the atmosphere and mixes with 12 CO2 and 13CO2. Carbon dioxide is usedplants during photosynthesis and from there through the food chain. Therefore, every plant and animal in this chain (including humans) will have an equal amount of 14C compared to 12C in the atmosphere (ratio14S:12S).
Method limitations
When living beings die, tissue is no longer replaced and radioactive decay 14C becomes apparent. After 55,000 years, 14C decays so much that its remains cannot be measured.
What is radiocarbon dating? Radioactive decay can be used as a "clock" since it is independent of physical (eg temperature) and chemical (eg water content) conditions. Half of the 14C contained in the sample decays in 5730 years.
Therefore, if you know the ratio 14C:12C at the time of death and today's ratio, then you can calculate how much time has passed. Unfortunately, it is not so easy to identify them.
Radiocarbon analysis: margin of error
The amount of 14C in the atmosphere, hence in plants and animals, has not always been constant. For example, it varies depending on how many cosmic rays reach the Earth. It depends on solar activity and the magnetic field of our planet.
Fortunately, it is possible to measure these fluctuations in samples dated by other methods. You can count the annual rings of trees and the change in their contentradiocarbon. 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 with this method. Most, if not all, organic compounds allow radiocarbon dating. Some inorganic materials, such as the aragonite component of shells, can also be dated, since carbon-14 was used in the formation of the mineral.
Materials that have been dated since the inception of the method include charcoal, wood, twigs, seeds, bones, shells, leather, peat, silt, soil, hair, pottery, pollen, wall paintings, coral, blood remains, fabric, paper, parchment, resin and water.
Radiocarbon analysis of a metal is not possible if it does not contain carbon-14. The exception is iron products, which are made using coal.
Double count
Because of this complication, radiocarbon dates are presented in two ways. Uncalibrated measurements are given in years prior to 1950 (BP). Calibrated dates are also presented as BC. e., and after, as well as using the calBP unit (calibrated up to the present, before 1950). This is a "best estimate" of the actual age of the sample, but it is necessary to be able to go back toold data and calibrate them as new studies keep updating the calibration curve.
Quantity and quality
The second difficulty is the extremely low prevalence of 14С. Only 0.0000000001% of the carbon in today's atmosphere is 14C, making it incredibly difficult to measure and extremely sensitive to pollution.
In the early years, radiocarbon analysis of decay products required huge samples (eg, half a human femur). Many laboratories now use the Accelerator Mass Spectrometer (AMS), which can detect and measure the presence of various isotopes, as well as count individual carbon-14 atoms.
This method requires less than 1 gram of bone, but few countries can afford more than one or two AMS, which cost more than $500,000. For example, Australia has only 2 of these instruments capable of radiocarbon dating, and they are beyond the reach of much of the developing world.
Cleanliness is the key to accuracy
In addition, the samples must be carefully cleaned of carbon contamination 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 pollutant, it will be dated as 40,000 years old.
For this reason, researchers are constantly developing newmethods for efficient cleaning of materials. They can have a significant impact on the result that radiocarbon analysis gives. The accuracy of the method has increased significantly with the development of a new method of cleaning with activated carbon ABOx-SC. This made it possible, 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 have passed since the beginning of the Earth, mentioned in the Bible, has been repeatedly criticized by creationists. For example, they argue that within 50,000 years samples should be free of carbon-14, but coal, oil, and natural gas, believed to be millions of years old, contain measurable amounts of this isotope, which is confirmed by radiocarbon dating. The measurement error in this case is greater than the background radiation, which cannot be eliminated in the laboratory. That is, a sample that does not contain a single radioactive carbon atom will show a date of 50 thousand years. However, this fact does not call into question the dating of the objects, and even more so does not indicate that oil, coal and natural gas are younger than this age.
Also, creationists note some oddities in radiocarbon dating. For example, the dating of freshwater molluscs has determined their age to be in excess of 2,000 years, which, in their opinion, discredits this method. In fact, it has been found that shellfish get most of their carbon from limestone and humus, which are very low in 14C, as these minerals are very old and do not have access toair carbon. Radiocarbon analysis, the accuracy of which in this case can be questioned, is otherwise true. Wood, for example, does not have this problem, because plants get carbon directly from the air, which contains a full dose of 14C.
Another argument against the method is the fact that trees can form 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, from which most measurements are based, has 5% fewer rings than its actual age.
Setting the date
Radiocarbon analysis is not only a method, but exciting discoveries 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 careful archaeologists linked pottery and stone tools from different geographical areas by looking for similarities in shape and patterns. Then, using the idea that object styles evolved and became more complex over time, they could place them in order.
Thus, the large domed tombs (known as tholos) in Greece were considered to be the forerunners 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, inAs a result of radiocarbon analysis, it turned out that the Scottish tombs were thousands of years older than the Greek ones. Northern barbarians were capable of designing complex structures similar to classical ones.
Other notable projects were 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 the drawings in the Chauvet Cave at 38,000 calBP (about 32,000 BP), thousands of years earlier than expected.
Radiocarbon analysis has also been used to determine the timing of the extinction of the mammoths and has contributed to the debate over whether modern humans and Neanderthals met or not.
Isotope 14С is used not only to determine age. The method of radiocarbon analysis allows us to study the circulation of the ocean and trace the movement of drugs throughout the body, but this is a topic for another article.
