The New Zealand physicist Ernest Rutherford, suggested in 1905 that the exact age of a rock could be measured by means of radioactivity.For the first time he was able to exactly measure the age of a uranium mineral.
The Potassium-Argon dating method is the measurement of the accumulation of Argon in a mineral.
It is based on the occurrence of a small fixed amount of the radioisotope Ar with a half-life of about 1,300 million years.
As a result it is always undergoing natural radioactive decay while the abundances of the other isotopes are unchanged.
Carbon-14 is most abundant in atmospheric carbon dioxide because it is constantly being produced by collisions between nitrogen atoms and cosmic rays at the upper limits of the atmosphere.
Shortly after Becquerel's find, Marie Curie, a French chemist, isolated another highly radioactive element, .