Dr Alan Smith
Cambridge geologist who helped lay the groundwork for the scientific acceptance of plate tectonics
DR ALAN SMITH, who has died aged 80, was an eminent geologist best known for the 1965 paper “The fit of the continents around the Atlantic”, published with Sir Edward Bullard and Jim Everett in Philosophical Transactions of the Royal Society of London, which laid the groundwork for the revelation, two years later, of the theory of plate tectonics – a major paradigm shift in the earth sciences.
The fit of the American continental coastline with the African and European ones had been noted ever since cartographers first charted them, though it was not until 1912 that the first complete account of the theory of continental drift was published by the German geophysicist Alfred Wegener.
Wegener had amassed evidence from fossils, and geological and geographical continuities between the continents, and postulated that they were once joined in a supercontinent called Pangaea, but subsequently broke up and drifted apart. Wegener envisaged the Earth as a series of shells, with the less dense outermost shell forming the continents floating on a denser ocean floor and responding to forces created by the planet’s rotation and to tidal pull from the Sun and Moon.
Wegener’s theory, however, ran counter to the dominant geological theory, which held that continents formed when the Earth cooled and have remained fixed in the same positions ever since. Until the middle of the 20th century neither theory prevailed, though continental drift seemed the less plausible, not least because the fit between the continents did not seem close enough to be convincing and because the mechanisms invoked by Wegener to explain the process were too weak.
By the 1960s the main protagonists in the debate included the eminent Cambridge mathematician and geophysicist Sir Harold Jeffreys for the “fixists”, and the Tasmanian geologist Warren Carey, an advocate of continental drift, who in 1958 first showed that there is a close visual fit between the (2,000 metre – approximately 1,000 fathom) submarine contours of western Africa and eastern South America. Jeffreys still denied that there was a fit, but his Cambridge colleague Bullard, head of the small department of geodesy and geophysics, though himself sceptical about continental drift, set his PHD student, Everett, the task of quantifying the “fit” using the early Cambridge University mainframe computer EDSAC 2.
Everett wrote a program that not only fitted together any two wiggly lines on a sphere, but also showed the relationship between the continents at different submarine depths. He was soon joined by Smith, then a research assistant in Bullard’s department, who provided much-needed geological expertise. Though both men had been sceptical of continental drift, they achieved almost perfect fits at the 500 fathom line (approx 900m).
Their map showed, conclusively, that the continents around the Atlantic were once contiguous, and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic period. Their paper was subsequently cited more than 1,000 times in refereed journals. Though the phenomenon it described became known as the “the Bullard fit”, it was Smith and Everett who achieved it.
At about the same time that they were working on their study, other scientists were assembling evidence, from magnetic anomalies on the ocean floor, that the sea floor must have “spread” out from so-called “spreading ridges” such as the Mid-atlantic Ridge and the East Pacific Rise, causing the continents to move apart. All this evidence, both from the ocean floor and from the continental margins, made it clear that continental drift was feasible, and the theory of plate tectonics, which was defined in a series of papers between 1965 and 1967, was born.
Smith, a fellow of St John’s College, Cambridge, from 1970, taught geology to generations of Cambridge undergraduates. Through his career he taught most parts of the first year geology course, excepting only palaeontology, and took part in numerous field trips. There, as one former student recalled in a blog, he was “a master at asking those apparently simple questions that ultimately turn out to be the keys that unlock a problem, the ideas that turn conventional wisdom on its head and lead to ‘breakthrough thinking’”.
Alan Gilbert Smith was born on February 24 1937 in Watford, Hertfordshire. His father, Benjamin, was an engineer and inventor who made ball bearings for the Royal Navy in the Second World War. Alan was educated at Watford Grammar School.
After graduating from St John’s College, Cambridge, in natural sciences, he did graduate work on the stratigraphy of the Western US and Canada at Princeton, where Harry Hess was beginning to put together his ideas on ocean-floor spreading. At first Smith, who had been heavily influenced by Jeffreys at Cambridge, was sceptical of Hess’s work and of continental drift theory more generally. He returned to Cambridge, where he soon began his collaboration with Everett.
He joined the staff of the Department of Geology in 1964 and, with the help of improved computer programs, continued his work on continental fitting. Among numerous studies, he produced a fit of the ancient supercontinent of Gondwana (Smith and Hallam, 1970) that set the result in the new language of plate tectonics, and of the so-called Tethyan Belt (the convergence zone between the Indian and Eurasian tectonic plates) in a widely cited paper entitled “Alpine deformation and the oceanic areas of the Tethys, Mediterranean and Atlantic”, published in the GSA Bulletin in 1971. He also conducted detailed geological studies in Greece and combined them with extensive palaeomagnetic data to produce “Phanerozoic” world maps, showing the changing positions of continents over the past 545 million or so years.
One of his most important contributions was the production, with colleagues, of a series of books on geological time scale (1982, 1990 and 2004) that have become a fundamental reference source in the earth sciences.
Smith was a very humble man who never talked about his achievements. He served on many international committees and commissions, and won numerous awards including, in 2008, the Lyell Medal of the Geological Society of London, named after the great 19th century geologist
Sir Charles Lyell.
He was greatly respected and loved by colleagues and students, many of whom very recently came from around the world to help him to celebrate his 80th birthday. When word spread that he was seriously ill, he was visited every day by friends and colleagues.
In the early 1960s he married Judith Walton, whom he had met folk dancing at Princeton, where she worked for the University Press. She died in 2010 and he is survived by their daughter.