Carbon Dating

The Allahabad High Court recently ordered a “scientific survey”, including carbon dating, of a “Shivling” said to have been found at the Gyanvapi mosque complex in Varanasi after setting aside a lower court order on the issue.

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.

Radiometric dating methods –

• These are used to calculate the age of inanimate things. Instead of carbon, decays of other radioactive elements that might be present in the material become the basis for the dating method. Two commonly employed methods for dating rocks are —
  • • Potassium-argon dating — The radioactive isotope of potassium decays into argon, and their ratios can give a clue about the age of rocks.
    • Uranium-thorium-lead dating — 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 — It is used to determine how long an object has remained exposed to sunlight. It is regularly applied to study the age of ice cores in polar regions.