Question

Carbon-14 is used to determine the age of organic material. The procedure is based on the formation of ${}^{14}C$ by neutron capture in the upper atmosphere.
${}_7^{14}N{+}_0^{1}n{\to }_6^{14}C{+}_1{P}^1$
${}^{14}C$ is absorbed by living organisms during photosynthesis. The ${}^{14}C$ content is constant in living organisms once the plant or animal dies, the uptake of carbon dioxide by it ceases and the level of ${}^{14}C$ in the dead being, falls due to the decay which C-14 undergoes ${}_6^{14}C{\to }_7^{14}N+{\beta }^{-}$
The half-life period of ${}^{14}Cis5770yr.$
The decay constant $\left(\lambda \right)$ can be calculated by using the following formula $\lambda =\frac{0.693}{\frac{t_1}{2}}.$
The comparison of the ${\beta }^{-}$ activity of the dead matter with that of the carbon still in circulation
enables measurement of the period of the isolation of the material from the living cycle. The
method however, ceases to be accurate over periods longer than 30,000 yr. The proportion of ${}^{14}C$ to
${}^{12}C$ in living matter is $1:{10}^{12}.$
What should be the age of fossil for meaningful determination of its age?

• A. 6 yr
• B. 6000 y
• C. 60,000 yr
• D. It can be used to calculate any age

Answer 1

The correct option is B 6000 y

Fossil whose age is closest to half-life of C-14 (5770 yr) will yield the most accurate age by C-14 dating.