2017 President's Medal

Presented to Thure E. Cerling

Citation by Claudia I. Mora

Thure Cerling is a distinguished professor of both geology and biology at the University of Utah, which is just one clue that he is a man of broad scientific interests and achievements. His research has had enormous impact at the intersection of these disciplines and, in 2001, he was elected to membership in the National Academy of Sciences.

Thure never met an isotope he didn’t like! His research has examined numerous isotopic systems, with a general approach of first understanding isotopic behavior through fundamental principles and relationships, backed by experimental studies in modern systems, and ultimately applied to understand geological history. He has worked on K-Ar geochronology in the East African Rift Valley, and on the behavior of the whole suite of isotopes in radioactive waste and issues posed by its disposal. He worked with Harmon Craig on the use of helium-3, a cosmogenically produced isotope, to date rock surfaces, or, as he might put it, to determine when previously shielded rocks started to get their “cosmic ray suntan.” He started from scratch, of course, working out natural production rates for He-3, then applying his knowledge to understand lava dam bursts and massive floods in the Grand Canyon. These early studies helped to develop a much broader interest in the application of cosmogenic nuclides to resolve many longstanding problems in geomorphology. With Robert Poreda and Kip Solomon, he combined measurement of He-3 and H-3 (tritium) to determine the residence time of water in shallow groundwaters, and as tracers of groundwater mixing, another now-routinely applied scientific tool. His research has developed our understanding of stable isotopes in soil carbon and pedogenic carbonate, and carried over to the interpretation of pedogenic carbonates in fossil soils as a very widely applied paleo-atmospheric CO2 barometer, which has yielded results fundamental to our understanding of the rise and global influence of terrestrial vegetation. Seeking to reconstruct the history of C4 photosynthesis, Thure and his students demonstrated the robustness of carbon isotopes in fossil tooth enamel as a record of diet, consistent with the soil carbon record, that captured the rapid, global expansion of grasslands and savannahs in the Miocene, and significantly added to our understanding of the environments that supported hominid evolution. Thus, Thure’s work has demonstrated the interdependence of ecology, climate, and atmospheres and has given us a picture of an integrated paleo-world in which terrestrial ecosystems emerged and evolved. His field experiments have had him studying CO2 diffusion in deep snow, sampling carbonate in paleosols high in the Himalayan Mountains, plucking tail hairs off elephants in the African savannah, and even collecting his beard hair daily as he traveled from the U.S, to Mongolia, an early test of the forensic value of hair to constrain diet and geolocation, and of isotopic turnover rates in mammals.

One of Thure’s most impactful achievements may be the training of more than 700 young scientists— an entire generation of isotopologists!— through “Isocamp,” an intensive course he and colleague Jim Ehleringer have led for the past 21 summers, which trains students in the fundamental theory underlying stable isotope fractionation in terrestrial and marine eco- and geo!- systems. Thure Cerling is clearly a “Renaissance man,” widely knowledgeable and endlessly curious, a hypothesis that Thure himself might choose to test through the wise and logical application of isotopes! His accomplishments and selfless enthusiasm for science have inspired so many. For all of these reasons, I am extremely pleased to present the 2017 GSA President’s Medal to a most-deserving man, Dr. Thure Cerling.

2017 President's Medal — Response by Thure E. Cerling

I am greatly honored to accept the President’s Medal of the Geological Society of America. Thank you, Claudia Mora, for this honor. It is a great privilege to join others who have received this medal before me, and who have enhanced our profession in so many different ways.

I chanced to discover geology after starting my college career in engineering. As it turns out, that quantitative background served me well in exploring questions that linked isotope geochemistry with biology, ecology, paleontology, and anthropology. My parents encouraged me to go in any direction, which allowed me the freedom to carve a wide path for myself. The support of my parents and siblings during my undergraduate studies at Iowa State and graduate studies at the University of California at Berkeley was crucial. So, too, was the support of faculty mentors Don Biggs, Carl Vondra, and Harry Svec at Iowa State. During my time at UC-Berkeley, Garniss Curtis, Dick Hay, and Chuck Meyer provided key support and guidance. I was privileged to be among the students Jim O’Neil welcomed into his stable isotope lab at the U.S. Geological Survey in Menlo Park; we spent many days and evenings discussing isotope geochemistry.

None of my work could have been done without the support of my wife and family. They have joined me in exploring many far-flung places and it has been a great joy to share field and cultural experiences with them. My children, Claire and Dylan, went on many unconventional camping trips and made field work even more enjoyable. And for the past twelve years, Mahala has been a partner in my sometimes unconventional travels.

If there is a common theme to my work it has been using isotopes to probe the secrets of the terrestrial environment. I have been fortunate to work in East Africa on problems of human evolution by developing quantitative methods by which we might better understand the environments in which humans evolved. Questions about those environments span the fields of anthropology, geology, botany, and conservation biology. It was through collaborations with many colleagues in the field and at the University of Utah that I was able to work on the many problems that Claudia outlined.

Harmon Craig and Karl Turekian provided great inspiration and guidance—“even the wrong road leads somewhere” (Harmon’s favorite quote from George Bernard Shaw), and “if you don’t get the answer you expect, maybe something more interesting is happening” have both proved to be excellent words of wisdom.

My Utah colleague Frank Brown, who died unexpectedly a short time ago, insisted on “looking where no one else has looked.” That idea, shared with me during field seasons in which we worked in the hot African sun during the day and talked for many hours under starry desert skies at night, led to new insights and paths to follow. I will greatly miss his deep friendship. Jim Ehleringer, another University of Utah colleague, has been a wonderful collaborator at the intersection of the geosciences and biosciences and we have spent many hours learning from each other.

For most of my career, I have been working at the triple junction of field geology, laboratory studies, and theoretical work. As an undergraduate, I was fascinated with isotopes, and they still lead me in new and sometimes unexpected directions. My study of soils started at Iowa State, progressed to field sites on paleosols in East Africa and Pakistan, and then to field studies on modern soils in the United States. Today I am working on high-resolution laminated soil carbonates in central Utah. Basic geological mapping, correlation of volcanic ash using trace element analyses, and dating using K-Ar in East Africa, in a region where no previous geology had been done, together made a great foundation for field studies that benefitted from collaborations across the fields of anthropology, paleontology, and geology. Having the opportunity to work at Oak Ridge National Lab gave me a unique insight into how anthropogenic isotope tracers can be used. Cosmogenic isotopes, especially Helium-3, opened new ways to think about the Quaternary—we could date specific events, such as landslides or rockfalls, that previously were not possible to date. Working on the giant floods of the Grand Canyon, formed by the failure of lava dams in the main canyon, provided insight into how catastrophic events can shape landforms. Working on the question of how isotopes can shed light onto ancient diets of mammals has led to wildlife conservation studies which now include anti-poaching and the illegal wildlife trade. As an undergraduate, I would never have thought my work might lead to meetings with Interpol! Studying the fundamental processes controlling the isotope systematics of plants, animals, and industrial processes led naturally to forensics studies. So I have been fortunate in being able to follow my interests, ideas, and passions in sciences. I was once told that if someone followed my career path they would end up in a ditch! Well, I am still here, and probably my good colleagues and students have kept me out of the ditch; I owe a huge debt of gratitude to each and every one of them.

My association with the sciences has given my life rich intellectual and personal depth. I have long believed that a huge part of our role as members of the academic community is to provide opportunities for young people. Since 1996, Jim Ehleringer and I have taught a two-week short course in stable isotope ecology (affectionately known as “IsoCamp”) at the University of Utah. Because our goal has been to show next-generation scientists the breadth of the stable isotope field, we have encouraged them to join us in approaching their explorations with an intellectual curiosity that includes many disciplines. We try to practice what we preach: colleagues from many different fields and academic institutions join us each year in IsoCamp. Some of these dedicated colleagues been part of the stable isotope ecology short course for more than 20 years.

Claudia, thank you and the Geological Society of America again for this extraordinary award. I am honored to accept it and to share it with my adventurous colleagues past, present, and future.