In 1913 Holmes was on the staff of Imperial College, when he published his famous book The Age of the Earth in which he argued strongly in favour of the use of radioactive dating methods rather than methods based on geological sedimentation or cooling of the earth (many people still clung to Lord Kelvin's calculations of less than 100 million years).
En 1913 Holmes traballaba no Imperial College, cando publicou o seu famoso libro The Age of the Earth no cal argumentaba decididamente a prol do uso dos métodos de datación radiométrica en lugar de métodos baseados na sedimentación xeolóxica ou do arrefriamento da Terra (moita xente daquela aínda se atiña aos cálculos de lord Kelvin dunha idade de menos de 100 millóns de anos).