What is radiocarbon analysis?

Radiocarbon analysis has changed our perception of the last 50,000 years. Professor Willard Libby first demonstrated it in 1949, for which he was later awarded the Nobel Prize.

Method of dating

The essence of radiocarbon analysis is the comparison of three different isotopes of carbon. The isotopes of a particular element have the same number of protons in the nucleus, but a different number of neutrons. This means that, with great chemical similarity, they have different masses.

The total mass of an isotope is denoted 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.

With time, ¹⁴ C - the basis of radiocarbon analysis - decomposes into nitrogen ¹⁴ N. Most of the carbon-14 is created in the upper atmosphere, where neutrons, which are formed under the action of cosmic rays, react with the atoms of ¹⁴ N.

Then it is oxidized in 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 it passes through the food chain. Therefore, any plant and animal in this chain (including humans) will have an equal amount of ¹⁴ C as compared to ¹² C in the atmosphere ( ¹⁴ C: ¹² C ratio).

Method Restrictions

When living things die, the tissue is no longer replaced, and the radioactive decay of ¹⁴ C becomes apparent. In 55 thousand years ¹⁴ C decays so much that its remains can not 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. For 5,730 years, half of the ¹⁴ C contained in the sample decays.

Therefore, if the ¹⁴ C: ¹² C ratio is known at the time of death and today's ratio, then it is possible to calculate how much time has passed. Unfortunately, it is not so easy to determine them.

Radiocarbon analysis: error

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, it is possible to measure these oscillations in samples dated by other methods. It is possible to calculate the annual rings of trees and the change in their content of radiocarbon. From these data, a "calibration curve" can be constructed.

Currently, work is under way to expand and improve it. In 2008, only radiocarbon dates could be calibrated to 26,000 years. Today the curve is extended to 50,000 years.

What can be measured?

Not all materials can be dated by this method. Most, if not all, of organic compounds allow for radiocarbon analysis. Some inorganic substances, such as the aragonite component of the shell, can also be dated, since carbon was used to form the mineral.

Materials that have been dated since the method was created include charcoal, wood, branches, seeds, bones, shells, skin, peat, silt, soil, hair, ceramics, pollen, wall paintings, corals, blood remnants, tissues, paper, Parchment, resin and water.

Radiocarbon analysis of the metal is impossible if it does not contain carbon-14. The exception is made of iron products, the manufacture of which uses coal.

Double account

Because of this complication, radiocarbon dates are presented in two ways. Uncalibrated 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 unit calBP (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 go back to the old data and calibrate it, as new research constantly updates the calibration curve.

Quantity and quality

The second difficulty is the extremely low prevalence of ¹⁴ C. Only 0.0000000001% of 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 the decomposition products required huge samples (for example, half of the human thigh bone). Many laboratories now use a mass spectrometer with an accelerator (AMS), which can detect and measure the presence of various isotopes, and also calculate the number of individual carbon atoms-14.

This method requires less than 1 g of bone tissue, but only a few countries can afford more than one or two AMS, the value of which exceeds $ 500 thousand. For example, Australia has only 2 such devices that are capable of producing 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 from carbon contamination from the adhesive and soil. This is especially important for very old materials. If 1% of the element in a sample 50 thousand years old will come from a modern polluter, it will be dated as a forty-year-old.

For this reason, researchers are constantly developing new methods for effective cleaning of materials. They can have a significant effect on the result, which gives radiocarbon analysis. The accuracy of the method has significantly increased with the development of a new method of cleaning with activated carbon ABOx-SC. This allowed, for example, to delay the date of arrival of the first people in Australia for more than 10 thousand years.

Radiocarbon analysis: criticism

The method, which proves that much more than 10 thousand years, mentioned in the Bible, has been repeatedly criticized by creationists since the time of the Earth's origin. For example, they argue that in the 50,000 years there should be no carbon-14 in the samples, but in coal, oil and natural gas, the age of which, presumably amounts to millions of years, contains measurable amounts of this isotope, which is confirmed by radiocarbon analysis. The measurement error is greater than the background radiation from which it is impossible to get rid of in the laboratory. That is, a sample in which no atom of radioactive carbon is contained will show a date of 50,000 years. However, this fact does not call into question the dating of objects and, moreover, does not indicate that oil, coal and natural gas are younger than this age.

Creationists also note some oddities in radiocarbon analysis. For example, the dating of freshwater mollusks determined their age as exceeding 2000 years, which, in their opinion, discredits this method. In fact, it is established that the mollusks receive most of the carbon from limestone and humus, the ¹⁴ C content in which is very low, since these minerals are very old and do not have access to carbon dioxide. Radiocarbon analysis, the accuracy of which in this case can be questioned, otherwise corresponds to reality. Wood, for example, has no such 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 capable of forming more than one ring in one year. This is true, but more often it happens that they do not form annual rings at all. A spruce pine, on the basis of which most of the measurements were taken, has 5% less rings than its actual age.

Setting a date

Radiocarbon analysis is not only a method, but also exciting discoveries in our past and present. The method allowed archaeologists to locate 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 pottery and stone tools of various geographical regions by searching for similarities in shape and patterns. Then, using the idea that the styles of objects evolved and became more complex with time, they could place them in order.

Thus, large domed tombs (known as tolos) in Greece were considered to be the precursors 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 innovations.

However, as a result of radiocarbon analyzes it was found that the Scottish tombs were thousands of years older than the Greek tombs. Northern barbarians were able to design complex structures, similar to classical ones.

Other notable projects included the Shroud of Turin to the medieval period, the dating of the Dead Sea scrolls by the time of Christ, and the somewhat controversial periodization of drawings in the Shove cave , which was 38,000 calBP (about 32,000 BP), thousands of years earlier than expected.

Radiocarbon analysis was also used in determining the extinction time of mammoths and contributed to the controversy over whether modern people and Neanderthals have met or not.

Isotope ¹⁴ C is used not only to determine the age. The method of radiocarbon analysis allows you to explore the circulation of the ocean and trace the movement of drugs throughout the body, but this is another topic.