Seminar Series – Dr. Emily M. Stewart: The Intertwined Fates of Lithospheric Carbon and Life on Earth

Dr. Emily M. Stewart, Florida State University

The Intertwined Fates of Lithospheric Carbon and Life on Earth

Planet Earth has supported life for billions of years. Despite dramatic changes in the surface environment and the deep Earth, our climate has remained relatively stable — and critically, habitable — over this time period. This stability is a result of the geologic Global Carbon Cycle, which acts to exchange carbon between the solid Earth, oceans, and atmosphere on timescales of ~1 million years or longer. Yet geological processes can also contribute to catastrophic instability, driving historic mass extinctions and rapid environmental change. 

 On the other hand, the evolution of life has profoundly altered the nature and distribution of carbon in the lithosphere over billions of years. Thus, the solid Earth and living organisms are locked in an evidently never-ending cycle of carbon exchange, each driving the evolution of the other. But how exactly do these spheres interact, and is all of this back-and-forth marching towards an end? 

We will explore a few aspects of this cycle from the perspective of a metamorphic petrologist. Rock metamorphism is an often-neglected part of the geologic carbon cycle, but I will argue that it may be of paramount importance to our planet’s habitability. Drawing examples from Acadian mountain-building, Mesozoic mass extinction, and Precambrian metamorphism, an observation-driven, field-based approach is used to quantify some of these interactions. Finally, a comprehensive study of an ancient subduction zone shows that metamorphism alone may release about half of all carbon from a subducting slab, perhaps driving progressive carbon depletion of the mantle over time and fundamentally altering the nature of global carbon cycling in eons to come. 

Host: GEO Faculty