Context: 

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.

About 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. 
• 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 stop. 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.

Determining the age of non-living things:

• Ineffectiveness 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 deduced 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: 

• • Two commonly employed methods for dating rocks are potassium-argon dating and uranium-thorium-lead dating. 
    • Uranium-lead dating: This method is used to date rocks and minerals that contain the minerals zircon or apatite, which incorporate uranium and lead into their crystal structure. Uranium-lead dating can date rocks that are billions of years old.
    • Potassium-argon dating: This method is used to date rocks and minerals that contain the mineral potassium feldspar. Potassium-argon dating can date rocks that are millions of years old.

News Source: Indian Express