What methods do archaeologists use to identify the age of ancient grains?

Archaeologists use carbon-14 dating to date ancient grains.

Carbon-14 dating, also known as radiocarbon dating, radiocarbon dating, etc.

Radiocarbon or carbon-14 is an unstable and weakly radioactive isotope of the element carbon. Carbon-14 is constantly formed in the upper atmosphere due to the action of cosmic ray neutrons on carbon-14 atoms. It oxidizes rapidly in the air, forming carbon dioxide and entering the global carbon cycle.

Plants and animals absorb carbon 14 from carbon dioxide throughout their lives. When they die, the exchange of carbon with the biosphere is immediately stopped, and their carbon-14 content begins to decrease, the rate of which is determined by radioactive decay. By knowing the amount of carbon-14 remaining in a sample, it is possible to know the age of the death of organic matter.

Carbon-14 is a radioactive isotope of carbon that was first discovered in 1940. It is produced by cosmic rays striking carbon 12 atoms in the air, and its half-life is about 5,730 years, and the decay mode is decay, and the carbon 14 atom is transformed into nitrogen atoms. Due to its half-life of 5,730 years and the fact that carbon is one of the elements of organic matter, we can infer the age of a dead organism based on the residual carbon 14 composition in the body.

When the organism is alive, due to the need to breathe, the amount of carbon 14 in its body is roughly unchanged, and the organism will stop breathing after death, and the carbon 14 in the body begins to decrease. For example, due to the frequent exchange with the atmosphere in the life process of terrestrial organisms and marine organisms, the decayed carbon 14 can often be replenished, but once the exchange is stopped (such as death, sedimentation), the carbon 14 can no longer be replenished, and the level of carbon 14 decreases due to decay, falling to half of the original level every 5730 years. Therefore, by measuring the existing level of carbon 14 radioactivity in a specimen compared to its original radioactivity level, it is possible to calculate the age of death or cessation of exchange.

Since the proportion of carbon isotopes in nature has always been stable, the approximate age of an antiquity can be estimated by measuring its carbon-14 content. This method is called carbon dating.

Other commonly used ones are potassium-argon determination, potassium-argon determination, thermoluminescence determination, etc.

Dating with the isotope 146c of carbon.

Archaeologists use carbon-14 dating to determine the carbonaceous material in the site and thus date food production. This assay is based on the principle that carbon, the ubiquitous building block of life, has a very small amount of radioactive carbon-14 in its composition, and carbon-14 decays into the non-radioactive isotope nitrogen-14.

Cosmic rays are constantly producing carbon-14 in the atmosphere. Plants absorb atmospheric carbon, with carbon-14 and the ubiquitous isotope carbon-12 maintaining a known almost constant ratio (about 1 to 1 million). The carbon in the plants then makes up the bodies of the herbivores that eat these plants, and also the bodies of the carnivores that eat these herbivores.

However, once these plants or animals die, half of their carbon-14 levels decay into carbon-12 every 5,700 years, until about 40,000 years later, when the carbon-14 levels become so low that they are difficult to measure, and it is difficult to distinguish them from being contaminated with small amounts of modern materials containing carbon-14. Therefore, the age of the material excavated from the archaeological site can be calculated based on the ratio of carbon-14 to carbon-12 within the material.