Carbon Dating

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• Recently, a court in Varanasi rejected a plea asking for a scientific investigation into the structure found inside the Gyanvapi Mosque that the Hindu side has claimed is a Shivling.
  • The dispute is now in the Supreme Court.  

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.

What about non-living things? / Radiometric dating methods

• Carbon dating cannot be applied in all circumstances. 
• 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 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.
• 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
    • 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.

Source: IE