Question

What should be the age of a fossil for the meaningful determination of its age?
(A) 6 years
(B) 600 years
(C) 6000 years
(D) It can be used to calculate any edge

Answer 1

Hint: To calculate the age of living organism that existed on this earth long ago carbon dating is a very useful method as we know the ratio of ${}_{6}^{14}C$ to ${}_{6}^{12}C$ in living matter is $1:{{10}^{12}}$ so we calculate the ${}_{6}^{14}C$ in the fossil of dead matter and that comparison of different ${}_{6}^{14}C$ values in living matter and dead matter, gives us the clear idea of the age of fossil.

Complete answer:
Fossils are the geological remains of a once-living organism. To calculate the age of fossils carbon dating method is used. Carbon- 14 is used to determine the age of fossils. The formation of ${}_{6}^{14}C$ by neutron capture takes place in the upper atmosphere. This ${}_{6}^{14}C$ is absorbed by living organisms.
\[{}_{7}^{14}N+{}_{0}^{1}n\to {}_{6}^{14}C+{}_{1}^{1}H\]
Since ${}_{6}^{14}C$ keeps decaying along with regular intake, its content stays constant in living organisms. Once the plant or animal dies, the uptake of carbon dioxide by it ceases and the level of ${}_{6}^{14}C$ in the dead organism falls due to the decay of${}_{6}^{14}C$.
\[{}_{6}^{14}C\to {}_{7}^{14}N+{{\beta }^{-}}\]
The half-life period of ${}_{6}^{14}C$ is 5760yr so decay constant can be calculated by using the formula
 \[\lambda =\dfrac{0.693}{{{t}_{1/2}}}\]
The comparison of the β- activity of the dead matter with that of the carbon still in circulation gives us the idea of the period of the isolation from the living cycle.
Carbon dating method is useful to determine the age of the fossils that are 6000 years or more old.

Correct answer is Option (C).

Additional information: In general Carbon dating method can be used to determine the age of the fossils that are older than carbon-14 half life or 5760 years old.

Note: Carbon-14 is produced in the upper layers of the troposphere and the stratosphere by thermal neutrons absorbed by nitrogen atoms. When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons. The resulting neutrons (1n) participate in the following n-p reaction:
\[{}_{7}^{14}N+{}_{0}^{1}n\to {}_{6}^{14}C+{}_{1}^{1}H\]
The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km and at high geomagnetic latitudes.