ARTHUR HOLMES: A 21st CENTURY LEGACY IN CONTINENTAL DRIFT

Regius Professor Arthur Holmes’ University of Edinburgh department has had a long lasting influence on the geological sciences. It was probably the only northern hemisphere center of study in the geological sciences to teach continental drift as a serious hypothesis during the 1950’s. The wide geographic scope of Holmes’ textbook Principles of Physical Geology, embracing continental drift and suggesting a mechanism in mantle flow, inspired many young workers to think in global terms. The topic of the first published contribution on pre-Pangea plate tectonics, J. Tuzo Wilson’s 1966 Nature contribution: “Did the Atlantic Ocean Open, Close and Open Again?,” was discussed at length in Alexander Cockburn’s lectures in the Grant Institute during the 1950’s. Thus the hypothesis of continental accretion, prevalent in North America during the late 1950’s and early 1960’s, made little sense to those of the Holmes school with knowledge of the strength of the evidence for drift and supercontinental fragmentation expounded by Alex du Toit and others from the southern hemisphere and summarized by Holmes, and to others aware of the existence of Archean rocks on the outermost Atlantic fringes of the Eurasian continent. For the past 20 years earth scientists have been attempting to unravel the puzzle that Holmes recognized in the first half of last century: when did Gondwanaland and Pangea come into existence, and were there earlier supercontinental entities? In the absence of oceanic lithosphere in the Neoproterozoic Pacific Ocean basin older than that in the Mesozoic-Cenozoic Atlantic basin, there is no ‘road map’ for pre-Pangea continental drift. The paleomagnetic data that Holmes immediately recognized as the first geophysical support for the very existence of the process of continental drift in the Mesozoic and Cenozoic demonstrate pre-Pangea drift to be a reality, but it is geological data of the type used by Holmes and Du Toit to support Pangea reconstructions that must be used to reconstruct pre-Pangea drift geography, and it is the isotopic data first brought to the forefront by Holmes early last century that is providing critical support.