1910. 1912 saw Holmes on the staff of Imperial College, publishing his famous book The Age of the Earth in 1913 in which he argued strongly for radioactive methods compared with methods based on geological sedimentation or cooling of the earth (many people still clung to Lord Kelvin's calculations of less than 100 Ma). He estimated the oldest Archean rocks to be 1,600 Ma, but did not speculate about the Earth's age. By this time the discovery of isotopes had complicated the calculations and he spent the next years grappling with these. His promotion of the theory over the next decades earned him the nickname of Father of modern geochronology. By 1927 he had revised this figure to 3,000 Ma and in the 1940s to 4,500±100 Ma, based on measurements of the relative abundance of uranium isotopes by Alfred O. C. Nier. The general method is now known as the Holmes-Houterman model after Fritz Houtermans who published in the same year, 1946. In 1924 he was appointed to the newly created post of reader in geology at Durham University. Eighteen years later his achievements were recognised, when he became a Fellow of the Royal Society in 1942. In the following year he was appointed to the chair of geology at the University of Edinburgh, following the death of Prof Thomas James Jehu, which post he held until retirement in 1956. In 1944 he published the first edition of his Principles of Physical Geology which became a standard textbook in the UK and elsewhere. Continental drift Holmes championed the theory of continental drift promoted by Alfred Wegener at a time when it was deeply unfashionable with his more conservative peers. One problem with the theory lay in the mechanism of movement, and Holmes proposed that Earth's mantle contained convection cells that dissipated radioactive heat and moved the crust at the surface. His Principles of Physical Geology ended with a chapter on continental drift. Part of the model was the origin of the seafloor spreading concept. Honours and awards Honours included: 1940 Murchison Medal, Geological Society of London 1946 Sederholm Medal, Geological Society of Finland 1955 Foreign Member Académie des sciences, Institut de France 1956 Penrose Medal, Geological Society of America 1956 Wollaston Medal, Geological Society of London 1962 Makdougall Brisbane Medal, Royal Society of Edinburgh 1964 Vetlesen Prize, Columbia University The Arthur Holmes Medal of the European Geosciences Union and a