Citation by Zachary Sharp
I am delighted to introduce Thure Cerling as the 2025 Penrose medalist. Thure is the most creative and innovative scientist I know. He not only works on important problems but literally creates new fields of research. He pioneered the use of soil carbonates for paleoclimate reconstruction and estimating atmospheric CO2 abundances. He developed the concept of using fossil bioapatite for paleoecological studies. Thure and his colleagues discovered a widespread increase in C4 plant production 6 to 8 million years ago using soil carbonates and fossil tooth enamel. Everyone knows of Thure’s outstanding scientific contributions, but those of us who know him personally can add to that. Thure is a generous, kind person, with a wicked sense of humor. He is always there to help and share ideas. My year with Thure in Switzerland was an unforgettable experience. Thank you, Thure, for your friendship, and congratulations on an award most well-deserved.
Response by Thure E. Cerling
Carl Sandburg, one of my favorite authors, said of his growing up in Galesburg, Illinois, “in nearly every life come sudden little events not expected that change its course.” For better or worse, my life has been full of such events!
Moving from a Chicago suburb to a small town in Iowa the summer before my sophomore year in high school, I found myself transported into academic purgatory. Unbendable rules made it impossible for me to enroll in math and science courses appropriate to what I’d already studied. Assuming I was not cut out for college-level work, my guidance counselor put me in typing, drafting, and remedial reading. Determined to leave small-town life behind, I worked three part-time jobs throughout my remaining high school years and saved enough money to enroll at Iowa State in the fall of 1967. Majoring in engineering science and nuclear engineering, I happily took modern poetry, Shakespeare, and Chaucer for my filler classes.
What if I’d been drafted into the Vietnam War? What if my older sisters hadn’t each met and married Iowa State geology students? Would I ever have discovered geology?
Geology: here was a discipline where mathematics, chemistry, physics, observation, and, yes, drafting skills—were all part of the package. Rigorous training in all the sciences meant I didn’t have to make a choice! I could continue to explore without academic boundaries. I had found my intellectual home.
While still an undergraduate, I had an unexpected opportunity to work in the Turkana Basin, a vast region in northern Kenya that had never been mapped. It was also the site of the Leakey expeditions. When I arrived at the remote field camp, where facilities were primitive, logistics difficult, and lions occasionally wandered through after dusk, I was introduced not just to other geologists, but to paleontologists and anthropologists. We were all exploring questions related to hominin evolution, further broadening my scientific horizons.
Back at Iowa State, Harry Svec introduced me to the field of stable isotopes and surprised me with an offer of two mass spectrometers to use for my master’s thesis. The catch? I had to scavenge parts from one machine to make the other work! Later, while a PhD student at Berkeley, I worked with Garniss Curtis and Jim O’Neil; what I didn’t fully realize at the time was just how new the fields of K-Ar dating and stable isotope geochemistry were, and that I was having opportunities to work with visionary pioneers. My first sabbatical leave from the University of Utah, the institution where I spent my academic career, took me to work at the lab of the legendary, if somewhat irascible, Harmon Craig at Scripps. It might surprise you to know he would stop lab meetings to chat amicably, and at length, with my young daughter about her day at school. And it was in Harmon’s lab that my son, age three, looked up at a fire extinguisher and asked, “Why do scuba divers wear those on their backs?”
An impossible question, for sure, but not the only one I’ve fielded over the years! Much of my career has been involved in exploring questions about hominin evolution. From correlating volcanic ash to reconstructing the diets of early hominins, my interests in reconstructing paleoenvironments continued to broaden, eventually encompassing forensics and wildlife conservation. A random question asked by a colleague in the extreme heat of a typical afternoon, “Do you think this stone tool was made by someone sitting in the shade?” was yet another impossible question thrown my way. Answering it eventually led to a paper that quantified the amount of shade that would have been available to hominins near the shores of Lake Turkana. Reconstructing the diets of those early hominin ancestors required the development of modern analogs and the sampling of teeth, hair, and feces from animals the size of mice to elephants. Did I ever think I would be sampling mouse breath or elephant tail hairs when I was back at Iowa State?
At the University of Utah, I have enjoyed the freedom to grow as a scientist and researcher as my interests have grown. Along the way, I have shared collaborations with Utah colleagues Frank Brown, Jim Ehleringer, and Kip Solomon. Often our discussions have been variations on a theme: how could field observations, lab experiments, and more precise calculations be used to refute—not preemptively prove—a theory? Approaching experiments and the resulting datasets with this perspective has, I think, allowed me to view results objectively and change course or improve methodologies along the way. Speaking of perspectives, I would be remiss not to mention the extraordinary changes that have happened in laboratory technologies—smaller sample sizes, faster run times, better vacuum pumps—and computational capacities. What a long road from slide rules, drafting tables, typewriters, paper maps, and Brunton compasses!
Some things haven’t changed. A geologic hammer, hand lens, reliable transportation, and fifty feet of rope (because you never know) are still useful in the field. My travels to collect and measure samples have literally taken me around the globe; I have worked with students and colleagues from many different scientific disciplines and backgrounds. Unlikely adventures, inhospitable conditions, and long conversations under the stars have provided me with lifelong friendships and fueled my creative energies. I have been fortunate to share my passion for geology, physics, mathematics, biology, chemistry, and the written word with students and colleagues as, together, we explored all kinds of impossible questions in the field, in the lab, and on the backs of napkins and envelopes.
My parents instilled in me a love of both wordplay and hard work, things I hope I have shared with my children, their children, and with my extended scientific family.