Arthur Holmes (14 January 1890 – 20 September 1965) was an English geologist who made two major contributions to the understanding of geology. He pioneered the use of radiometric dating of minerals, and was the first earth scientist to grasp the mechanical and thermal implications of mantle convection, which led eventually to the acceptance of plate tectonics. Life He was born in Hebburn, County Durham, near Newcastle upon Tyne, the son of David Holmes, a cabinet-maker, and his wife, Emily Dickinson. As a child, he lived in Low Fell, Gateshead, and attended the Gateshead Higher Grade School (later Gateshead Grammar School). At 17, he enrolled to study physics at the Royal College of Science (now Imperial College London), but took a course in geology in his second year, which settled his future, against the advice of his tutors. Surviving on a scholarship of £60/year was difficult and on graduating hall, he took a job prospecting for minerals in Mozambique. After six months, with no discoveries, he became so ill with malaria that a notice of his death was posted home. However, he recovered enough to catch the boat home and became a demonstrator at Imperial College. He obtained his Doctorate of Science in 1917, and in 1920 he joined an oil company in Burma as chief geologist. The company failed, and he returned to England penniless in 1924. He had been accompanied in Burma by his three-year-old son, who contracted dysentery and died shortly before Holmes's departure. He was head of the Department of Geology, Durham University, 1924–1943. He held the chair of geology at the University of Edinburgh from 1943–1956. Holmes died at 20 St John's Avenue in Putney, London, on 20 September 1965. He was 75. Personal life He married his first wife, Margaret Howe, in 1914. After she died in 1938, Holmes in the following year married Doris Reynolds, a geologist who had joined the teaching staff at Durham. After his death, she edited the third edition of the Principles. Age of the earth Holmes was a pioneer of geochronology, and performed the first accurate uranium-lead radiometric dating (specifically designed to measure the age of a rock) while an undergraduate in London, assigning an age of 370 Ma to a Devonian rock from Norway, improving on the work of Boltwood who published nothing more on the subject. This result was published in 1911, after his graduation in