The Allahabad High Court ordered a “scientific survey”, including carbon dating, of a “Shivling” said to have been found at the Gyanvapi mosque complex in Varanasi.
What is carbon dating?
- Carbon dating is a widely-used method to establish the age of organic materials, things that were once living.
- Living things have carbon in them in various forms.
- The dating method is based on the fact that Carbon-14 (C-14), an isotope of carbon with an atomic mass of 14, is radioactive, and decays at a well known rate. This is how it works:
- The most abundant isotope of carbon in the atmosphere is C-12.
- A very small amount of C-14 is also present.
- The ratio of C-12 to C-14 in the atmosphere is almost static, and is known.
- Plants get their carbon through photosynthesis; animals get it mainly through food.
- Because plants and animals get their carbon from the atmosphere, they too acquire C-12 and C-14 in roughly the same proportion as is available in the atmosphere.
- When they die, their interactions with the atmosphere stops.
- While C-12 is stable, the radioactive C-14 reduces to one half of itself in about 5,730 years — known as its ‘half-life’.
- The changing ratio of C-12 to C-14 in the remains of a plant or animal after it dies can be measured, and can be used to deduce the approximate time when the organism died.
Limitations of carbon dating:
- It cannot be used to determine the age of non-living things like rocks.
- The age of things that are more than 40,000-50,000 years old cannot be arrived at through carbon dating.
- This is because after 8-10 cycles of half-lives, the amount of C-14 becomes almost very small and is almost undetectable.
- Instead of carbon, decays of other radioactive elements that might be present in the non-living material become the basis for the dating method.
- These are known as radiometric dating methods.
- Many of these involve elements with half-lives of billions of years, which enable scientists to reliably estimate the age of very old objects.
- Two commonly employed methods for dating rocks are potassium-argon dating and uranium-thorium-lead dating.
- The radioactive isotope of potassium decays into argon, and their ratios can give a clue about the age of rocks.
- Uranium and thorium have several radioactive isotopes, and all of them decay into the stable lead atom.
- The ratios of these elements present in the material can be measured and used to make estimates about age.
Cosmogenic nuclide dating:
- There are also methods to determine how long an object has remained exposed to sunlight.
- These are again based on radioactive decays and are particularly useful in studying buried objects or changes in topology.
- The most common of these is called cosmogenic nuclide dating, or CRN, and is regularly applied to study the age of ice cores in polar regions.
SOURCE: THE HINDU, THE ECONOMIC TIMES, PIB