THOMAS R. WORSLEY AND THE SUPERCONTINENT CYCLE

Over the past two decades, data from a wide variety of sources have led to the realization that Pangea was just the most recent in a series of supercontinents that have punctuated Earth history for billions of years. This record of episodic supercontinent assembly and breakup is now recognized to have profoundly influenced Earth’s geologic, climatic and biological evolution. The supercontinent cycle documents a fundamental aspect of Earth dynamics and its recognition is arguably the most important development in Earth Science since plate tectonics.

Often overlooked in this exciting development is its progenitor, T.R. Worsley, who first proposed the existence of such a cycle in 1982 (EOS, 63 (45), 1104). Although advocacy of long-term episodicity in tectonic processes predates plate tectonics, Worsley was the first to link such episodicity to the cyclic assembly and breakup of supercontinents. Contending that such a cycle would be manifest by peaks in collisional orogenesis lagged by rift-related mafic dike swarms, Worsley and his colleagues used available (Rb/Sr) data to argue that such episodes had punctuated Earth history at intervals of ~500 m.y. for at least the past 2.5 billion years. They predicted the existence of five supercontinents at ca. 0.6, 1.1, 1.7, 2.1 and 2.6 Ga (AGU Geophys. Monogr. 32, 1985, 561-572), the dates of four of which correspond to the amalgamation of Gondwana, Rodinia, Columbia and Kenorland.

For the Phanerozoic, they modeled the cycle’s influence on sea level by estimating the independent effects of sea floor elevation on ocean basin volume and epeirogenic uplift on continental platform elevation, and showed that predicted water depths at the shelf break closely matched first-order Phanerozoic sea level change for a supercontinent cycle of ~440 Ma duration (Mar. Geol., 1984, 58, 373-400). They also explored the cycle’s influence on tectonic trends, platform sedimentation, ice ages and global climate, major events in biogenesis, the marine stable isotope record and a wide range of biogeochemical signals (Paleoceanogr., 1986, 1, 233-263). That many of these influences have been borne out by more recent research and most of the predicted supercontinents (now defined more precisely by U-Pb geochronology) have been named is a testament to this early work and a tribute to the concept’s originator.