Hildebrand Fellow Joshua Zimmt Pieces Together the Link Between Climate Change and the First Mass Extinction of Animal Life

January 17, 2023

Joshua Zimmt is a Ph.D. candidate in the Department of Integrative Biology and UC Museum of Paleontology at UC Berkeley. He holds a B.S. in geology from the College of William & Mary. His research focuses on the link between climate change and its impact on the history of life, integrating geological, paleobiological, and geochemical data into a comprehensive understanding of past events. He received a Hildebrand Graduate Research Fellowship in Summer 2022 to study the link between climate change and mass extinction during the first mass extinction of animal life.

Climate change is one of the most pressing issues in the world today: the effects of our warming planet are all around us, with worsening droughts, rising sea levels, and catastrophic weather events featured across the news. Climate scientists have developed sophisticated models that can predict how and why this warming trend will worsen in the years to come. However, these models cannot tell scientists what the impact of global warming will be on species and ecosystems around the world. This gap in our knowledge is critical for adapting to and planning for our changing planet. Fortunately, we can use the fossil record to study past episodes of climate change and how they affected life on Earth to better understand the impact of modern
climate change on the natural world.

As a paleobiologist, I am motivated by the promise of using the past to help contextualize the present and make predictions about the future. In my work, I combine the disciplines of geology, biology, and chemistry to produce integrative perspectives of climate-driven events throughout the history of life. Investigating the geologic and fossil records of these events provides us with case studies of how life on Earth responds to climate change, but the interpretation of these events is complicated by climate-driven changes in sea levels that shape the geologic record. To solve this problem, I have developed a new method of studying the geologic and fossil records that combines high-resolution data from across a region into a comprehensive assessment of a climate-driven extinction event (Zimmt et al., 2021).

One of the most impactful climate-driven extinction events was the first major mass extinction of animal life, the Late Ordovician mass extinction. Nearly 445 million years ago, the Late Ordovician mass extinction eliminated ~80% of species diversity during a period of major climate change. The onset of the mass extinction is associated with global cooling and an abrupt fall in sea level, while the end of the event is associated with global warming and a rapid rise in sea level. However, it is not clear what aspect of climate change (cooling, warming, or some climate-driven change) drove the mass extinction. The application of my new method to the fossil and geologic records of the Late Ordovician mass extinction could therefore provide invaluable insight into this important extinction event.

To meaningfully apply my new method to the Late Ordovician mass extinction, I needed to choose a region with both exceptional fossil and geologic records. For over a century, Anticosti Island (Québec, Canada) has been visited by paleobiologists looking to study the Late Ordovician mass extinction. Across the 200-km long island, layers of rocks and fossils recording millions of years of life from an ancient ocean are beautifully exposed in coastal cliffs and river canyons. These qualities make Anticosti Island one of the best regional records of the Late Ordovician mass extinction and thus a promising target to implement my new approach for studying climate-driven mass extinctions.

The Hildebrand Fellowship provided me with the funding I needed to lead an international group of researchers from Stanford University, the University of Georgia, and the University of Ottawa for a month-long field season on Anticosti Island. Our goal was to develop a framework that would enable us to correlate the geologic record across my field sites so I could apply my method for studying climate-driven mass extinction events to the fossil and geologic records on Anticosti Island. The establishment of such a correlation framework would be a major step forward in our understanding of Anticosti Island. Despite more than a century of work preceding us, no such framework existed!

Over the course of the field season, we meticulously measured and described the geologic record of eastern Anticosti Island, visiting 17 field sites that spanned the Late Ordovician mass extinction. Our observations demonstrated that that the geologic record of Anticosti Island was far more complex than any researcher had previously recognized. We found evidence for several major climate-driven cycles in sea level during the Late Ordovician mass extinction, indicating a series of warming and cooling intervals during the extinction event. Working together, we were able to develop a framework that used these oscillations in sea level to correlate the geologic record across our field sites. This represents a critical step forward in our knowledge of one of the best regional records of the Late Ordovician mass extinction and will enable us to develop a high-resolution sequence of both climatic and biological events throughout the Late Ordovician mass extinction.

While this field season is the first step in applying my approach for studying climate-driven mass extinction events to the record on Anticosti Island, our findings have global significance. The recognition of several major warming and cooling cycles during the Late Ordovician mass extinction suggests that the traditional interpretation of the mass extinction is likely over-simplified and requires a more thorough assessment of the geologic and fossil records. Moving forward, I will incorporate geochemical and paleobiological data from my research into our new correlation framework. The integration of geological, geochemical, and paleobiological data into this framework will provide us with unprecedented resolution that we can then use to determine the relationship between climate change and the Late Ordovician mass extinction.

More information on Joshua's research on Anticosti Island can be found on the UC Museum of Paleontology site, here.