CARBON DATING - SCIENCE AND TECHNOLOGY
News: Gyanvyapi
dispute: Allahabad HC gives ASI more time to file reply on age evaluation of
‘Shivling’
What's in the news?
● The
Allahabad High Court granted one more chance to the Archaeological Survey of
India (ASI) to file its reply on whether carbon dating, ground penetrating
radar (GPR), excavation or any other method can be used for safe evaluation of
the age of the Shivling-like structure purportedly found inside the Gyanvapi
Mosque complex.
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.
Process of carbon dating:
● 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.
● Plants get their carbon
through the process of photosynthesis, while animals get it mainly through
food. 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.
What about non-living things?
● Though
extremely effective, carbon dating cannot be applied in all circumstances.
Specifically, 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 cannot be arrived at through carbon dating. This is because
after eight to ten cycles of half-lives have been crossed, the amount of
carbon-14 becomes almost negligible and undetectable.
● There
are other methods to calculate the age of inanimate things, but carbon dating
can also be used in an indirect way in certain circumstances.
● For
example, the age of the ice cores in glaciers and polar regions is determined
using carbon dating by studying the carbon dioxide molecules trapped inside
large ice sheets. The trapped molecules have no interaction with the outside
atmosphere and are found in the same state as when they were trapped.
Archaeological Survey of India (ASI):
● ASI
is the premier organization for the archaeological research, scientific
analysis, excavation of archaeological sites, conservation and preservation of
protected monuments.
● It
is an attached office under the Department of Culture (Ministry of Culture).
● ASI
was founded in 1861 by
Alexander Cunningham who became its first Director-General.
● It
also regulates the Antiquities and Art
Treasure Act, 1972.