Arthur Holmes, British geologist and geophysicist, obtained the degree Bachelor of Science (BSc) in physics at the Royal College of Science, London, in 1909. However, he was interested mainly in geology (having taken a course in the subject), particularly in the measurement of geological time. After graduating he accepted a contract appointment to prospect for minerals in Mozambique, but after six months had to return home suffering from malaria. His work in southern Africa none the less led to the following publications over the next few years: "Outlines of the geology of Mozambique" (Geological Magazine, 1912); "Mozambique: A geographical study" (with D.A. Wray, Geographical Journal, 1913); "The lateritic deposits of Mozambique" (Geological Magazine, 1914); "The Tertiary volcanic rocks of the District of Mozambique" (Quarterly Journal of the Geological Society, 1916); "The Pre-Cambrian and associated rocks of the District of Mozambique" (Geological Magazine, 1917); and some papers on the geology of Angola and the East African Rift Valley.
Upon his return to the United Kingdom Holmes was appointed as demonstrator of geology at the Imperial Collage, London (successor to the Royal College of Science). He obtained his Doctor of Science (DSc) degree in geology in 1917. In 1920 he became chief geologist to the Yomah Oil Company in Burma, but the company failed in 1922. From 1924 to 1942 he was the first reader in geology at Durham University. His publications during this period included papers on "The Gordonia uraninite and the upper Pre-Cambrian rocks of southern Africa" (American Journal of Science, 1934); "A contribution to the petrology of Kimberlite and its inclusions" (Transactions of the Geological Society of South Africa, 1936); and "Helium-ratios of rocks and minerals from the diamond pipes of South Africa" (Proceedings of the Royal Society of London, Series A, 1936). From 1943 to his retirement in 1956 he was professor of geology at the University of Edinburgh.
Holmes developed three major interests in geology and geophysics: Radiometric dating and the age of the earth; the petrology of igneous rocks, especially those of Africa; and the evolution of the earth. He was a pioneer of geochronology, who performed the first accurate uranium-lead radiometric dating by assigning an age of 370 Ma to a Devonian rock from Norway in 1911. From that time he spent many years refining the method and during the nineteen-forties derived an accurate estimate of the age of the earth. His major works included The age of the earth (1913, 1927, 1937, 1949); The nomenclature of petrology (1920, 1928); Petrographic methods and calculations (1921, 1923, 1930); The petrology of the volcanic field of Bufumbira, south-west Uganda (1937); and Principles of physical geology (1944 and later editions). The latter became a standard text-book in the United Kingdom and elsewhere. He was a supporter of the theory of continental drift and in 1927 proposed that its underlying cause was differential heating by radio-active decay that caused convection currents in the earth's mantle. Among his later publications relating to Africa were "The oldest dated minerals of the Rhodesian shield" (Nature, 1954) and African geochronology (1955).
Holmes was elected a Fellow of the Royal Society of London in 1942. His contributions to geology and geophysics were widely recognised. Among the awards he received were the Wollaston Medal (1956), Penrose Medal (1956) and Vetlesen Prize (1964). In 1914 he married Margaret Howe. After her death in 1938 he married Doris Reynolds, a geologist on the teaching staff at Durham University.