RADIO-CARBON
DATING – SCI & TECH
News:
Gyanvapi mosque case | SC
to hear plea against carbon dating of 'shivling'
What's
in the news?
● The
Supreme Court on Thursday agreed to urgently list a petition challenging an
Allahabad High Court direction to determine the age of the “shivling” allegedly
found in the Gyanvapi mosque premises at Varanasi through carbon dating.
Key
takeaways:
● The
High Court had ordered the authorities to ensure that no harm was done to the
edifice claimed to be a ‘shivling’.
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.