Carbon Dating

May 13, 2023

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.