A district court in Varanasi has allowed a petition seeking carbon dating of the structure inside the Gyanvapi mosque that the Hindu side has claimed is a ‘Shivling’.
What is carbon dating?
- Carbon dating is a widely-used method applied to establish the age of organic material, things that were once living.
- Living things have carbon in them in various forms. The dating method makes use of the fact that a particular isotope of carbon called C-14, with an atomic mass of 14, is radioactive, and decays at a rate that is well known.
- The most abundant isotope of carbon in the atmosphere is carbon-12 or a carbon atom whose atomic mass is 12. A very small amount of carbon-14 is also present. The ratio of carbon-12 to carbon-14 in the atmosphere is almost static, and is known.
- Because plants and animals get their carbon from the atmosphere, they too acquire carbon-12 and carbon-14 isotopes in roughly the same proportion as is available in the atmosphere.
- But when they die, the interactions with the atmosphere stops. There is no further intake of carbon (and no outgo either, because metabolism stops). Now, carbon-12 is stable and does not decay, while carbon-14 is radioactive. Carbon-14 reduces to one-half of itself in about 5,730 years. This is what is known as its ‘half-life’.
- So, after a plant or animal dies, the ratio of carbon-12 to carbon-14 in the body, or its remains, begins to change. This change can be measured and can be used to deduce the approximate time when the organism died.
What about non-living things?
- Though extremely effective, carbon dating cannot be applied in all circumstances. Specifically, it cannot be used to determine the age of non-living things, like rocks, for example.
- Also, the age of things that are more than 40,000-50,000 years cannot be arrived at through carbon dating. This is because after eight to ten cycles of half-lives have been crossed, the amount of carbon-14 becomes almost negligible and undetectable.
- There are other methods to calculate the age of inanimate things, but carbon dating can also be used in an indirect way in certain circumstances.
- For example, the age of the ice cores in glaciers and polar regions is determined using carbon dating by studying the carbon dioxide molecules trapped inside large ice sheets. The trapped molecules have no interaction with the outside atmosphere and are found in the same state as when they were trapped.
- How long a rock has been at a particular place can also be determined using similar indirect methods. If there are organic materials, dead plants or insects trapped beneath the rock, they can give an indication of when that rock, or any other thing, had reached that place.