Paul Gast, a geochemist at Lamont, had found good evidence that the source regions for ocean island basalts had to have been isolated for a billion years. “This seemed completely bizarre – how could you have a region which was in the convecting mantle and being stirred, how could it remain separate for 1000 million years?”, questioned McKenzie. “I thought this had to have some really important implications for what was happening in the mantle but because I’d only really done one year of geology, I knew essentially nothing at that stage about isotope geochemistry. So I did what I always do which is to try and work with people who do know better.” In this case it was Keith O'NionsKeith O'Nions (1944-present) is a British geochemist and academic specialising in the composition and evolution of the Earth. He held posts at Columbia University, the University of Cambridge and the University of Oxford before taking on policy and leadership roles. at Cambridge, for isotopeone of two or more species of the same chemical element that contain equal numbers of protons but different numbers of neutrons. geochemistry and Keith CoxKeith Cox (1933-1998) was a British geologist and academic at the University of Oxford. He had a particular interest in flood basalts and was regarded as one of the leading experts in this area. at Oxford for petrology.