Arthur Holmes and the Age of the Earth

Arthur Holmes (1890-1965)

Arthur Holmes (1890-1965)

On January 14, 1890, British geologist Arthur Holmes was born. Holmes 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.

Arthur Holmes was born in Hepburn, 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. 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 small scholarship was difficult and after graduation in 1910 he took a job prospecting for minerals in Mozambique. Unfortunately, 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 in 1912.

Holmes was a pioneer of geochronology, and performed the first accurate uranium-lead radiometric dating specifically designed to measure the age of a rock already while an undergraduate in London, assigning an age of 370 million years to a Devonian rock from Norway, improving on the work of Bertram Boltwood, the American pioneer of radiochemistry, who published nothing more on the subject. This result was published in 1911, a year after his graduation.

In 1913 Holmes published his famous book The Age of the Earth, 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 million years, while Holmes estimated the oldest Archean rocks to be 1,600 million years, 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 he earned the nickname of Father of modern geochronology. In 1917, at the age of 27 he received his doctorate of science from Imperial College as well. In 1920, Holmes joined an oil company in Burma as chief geologist. The company failed, and he returned to England penniless in 1924, but was appointed to the newly created post of reader in geology at Durham University. By 1927 he had revised his estimations to 3,000 million years and in the 1940s to 4,500±100 million years, 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.

Scientists were debating the validity and possibility of continental drift promoted by Alfred Wegener, when Holmes focussed on this problem at a time when it was deeply unfashionable with his more conservative peers. The main issue raised by many scientists is the mechanism by which the continents could move. Holmes major contribution was the hypothesis that the radioactive decay occurring in the mantle of Earth would generate heat, and thereby convection currents that would be the means by which the continents could move.[2] His Principles of Physical Geology (1944), which became a standard textbook in the UK and elsewhere, ended with a chapter on continental drift [3]. Part of the model was the origin of the seafloor spreading concept. Holmes was not a dogmatic adherent of Drift who was searching for a solution to the ‘mechanism’ problem. Rather, he was a sound geologist, who believed that there were enormous radioactive forces present in the earth’s interior which simply had to escape to the earth’s surface, and who recognized that these provided a solution to the ‘mechanism’ problem faced by Drift.[2]

In 1942 his achievements were recognised, when he became a Fellow of the Royal Society. In the following year he was appointed to the Regius Professor of Geology at the University of Edinburgh, which post he held until retirement in 1956. It was there, despite his declining health, that he completed some of his most important work on the age of the Earth, the geological time scale, the Precambrian, and the geology of Africa.[4] Holmes was awarded both the Wollaston Medal and the Penrose Medal in 1956, as well as the Vetlesen Prize in 1964, but at no presentation was his work on continental drift ever mentioned. [4] Arthur Holmes died in Putney, London on 20 September 1965, at the age of 75. The Arthur Holmes Medal of the European Geosciences Union is named after him.

At yovisto you can learn more about ‘Earth History in the Broadest Possible Context‘ in a lecture by Walter Alvarez at Berkeley University.

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