Sam Bowring’s expertise as a field geologist, his enormous breadth of knowledge, and his unwavering pursuit of the highest possible precision and accuracy in uranium-lead geochronology has transformed our understanding of the time when life began, the timing and triggers of the great mass extinctions, and the manner in which the Earth’s earliest crust evolved.
Sam determined the duration and rate of biological evolution at the Pre-Cambrian/Cambrian boundary—the so-called explosion of life that is the single most important evolutionary event in Earth history. Sam dated key volcanic strata within the sedimentary layers that record the Early Cambrian evolution of life and showed that the Cambrian period began 541 million years ago and that the Early Cambrian interval spanning the explosion of life lasted only 5 million to 6 million years. Sam showed that during this brief time interval more phyla than have ever since existed on Earth came into existence. This represents a truly profound and astonishing new discovery about how life evolved on Earth.
Sam has also established the timing and duration of the most significant biological extinction event in Earth history—the one defining the end of the Permian. Sam and colleagues have demonstrated that the extinction occurred in a time interval of less than 60,000 years and that the surge in light carbon predates the extinction by only 10,000 years. Having now established the precise timing of the extinction event and the global environmental crisis that preceded it, Sam has provided fundamental constraints on the forces that led to the environmental crisis resulting in the greatest extinction in Earth’s history.
Sam’s work on the world’s oldest rocks, the Acasta gneisses, has led to a new understanding of the processes leading to the early growth of continental crust. Through his rigorous field efforts in the Northwest Territories of Canada and his geochronological studies, Sam established that the Acasta gneisses were Priscoan in age (>4 billion years old). His geochemical studies of these early crustal remnants showed that these rocks were similar to today’s arc-derived continental crustal rocks, supporting the notion that crustal recycling started early on in Earth history and has continued to the present.
—Tim Grove, Massachusetts Institute of Technology, Cambridge