Soddy and Sir William Ramsay had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium.
Soddy e Sir William Ramsay acababan de determinar a taxa á que o radio produce partículas alfa, e Rutherford propuxo que podía determinar a idade dunha mostra de rocha medindo a súa concentración de helio.