The half life can serve as the molecular clock to determine the age of different products i.e., mineral, rocksand matter of vegetable origin such as wood, charcoal etc. because the half-life of a particlar nucleide is constant. C-14 being radio-isotope , it is also used to determine the age of different products. which is known as radio-carbon dating. C-14 is a neutron rich nucleide that decays by beta-emission with a half-life of 5730 years as under : ""_(6)^(14)C to ""_(7)^(14)N + ""_(-1)^(0)e Just after World War II . WIllcard F. Libby proposed a way to use this rection to determine the age of the carbon containing substances. The C-14 dating technique for which Libby received nobel is based upon the following assumption . (i) C-14 is produced in atmosphere at a more or less constant rate which is also equal to its rate of decay. As a result, there is a constant concentration of C-14 in the atmosphere and all living things. (ii) After death, organisms no longer pick C-14 (iii) By comparing activity of a sample with acitivity of living tissue we can estimate the age of organisms . One of the Libby's assumptions is questionable, the amount of C-14 has not been constant with time. It has varied as much as +- 5% . Charcoal sample emits 62.3% of disintegrations per gram of carbon per minute for living tissue. Then, what will be the age of charcoal ?