Rising to Challenges Beneath the Earth

David Kohlstedt ’65, Ph.D., professor emeritus at the University of Minnesota and graduate of the Valparaiso University physics department, has recently been named a recipient of the 2023 Vetlesen Prize for his work in recreating the conditions of Earth’s mantle for experimental investigation of the physical and chemical properties of rocks in a controlled laboratory environment. This international honor is given by the G. Unger Vetlesen Foundation for “scientific achievement resulting in a clearer understanding of the Earth, its history, or its relation to the universe.” Professor Kohlstedt will give the Vetlesen Lecture and receive a $250,000 prize at Columbia University in April.

Kohlstedt commented “There’s a great quote from Ernest Hemingway when he received the Nobel Prize in literature: ‘No writer who knows the great writers who did not receive the Prize can accept it other than with humility.’ There are a lot of extremely talented peers out there who could be receiving this award. I am truly honored.” He has previously been recognized with the Hess Medal from the American Geophysical Union in 2003 and by election to the National Academy of Sciences in 2009. 

For Professor Kohlstedt, the path to Valparaiso University had been laid out well before he finished high school. “My dad was a Lutheran minister, and my older sister, Pat (’63), was at Valpo before me, so there was a family tradition of going to Valpo on top of our strong Lutheran background,” he says. 

Professor Kohlstedt double-majored in physics and mathematics, and credits the excellent scientific education he received as playing a large role in his success, noting that six of his seven classmates in physics earned doctorates.  He particularly credits Professor Manuel Bretscher for peaking his interest in experimental physics. In addition, a well-rounded education that covered areas beyond his major further set his Valpo education apart. 

“The religion courses at that time were really thought-provoking. There was a lot of questioning and challenging that went on that made me reflect on foundational issues,” Professor Kohlstedt says. “In freshman English class we wrote an essay every week. Writing is extremely important if you’re going to do science, with papers and grants. One of my significant contributions to students, not always appreciated at the time, is correcting their grammar on papers.”

Valpo also holds a special place in his heart as the place where he met his wife, Sally (Gregory, ‘65). “We did a lot together, dating on and off from sophomore year on,” Professor Kohlstedt says. “A Friday night date might have been to sneak into some classroom building to find a place where we could do our homework for the weekend.”  Both highly motivated academically, they spent quiet and productive time together in the days when dorms were gender segregated.  

After graduation, Professor Kohlstedt’s academic journey took him to the University of Illinois, where he earned his Ph.D. in solid-state physics, and then overseas for a year of research in the Cavendish Laboratory at the University of Cambridge in England. Returning to the United States, he accepted a postdoctoral position in geophysics at the Massachusetts Institute of Technology (MIT) in order to be close to Sally, who joined the faculty at Simmons College. It was an exciting time in the earth sciences in the wake of the newly accepted paradigm of plate tectonics. At MIT he began to tackle the question of just how vigorously the mantle could convect in order to transfer heat from Earth’s core to its outer layers. 

“There were a number of problems that people hadn’t thought to look at, and thanks to my physics background I was pretty well-equipped to take them on,” Professor Kohlstedt says. “My approach has been to take the minerals that comprise a mantle rock, study their physical properties, and see what can be understood, then build the system up and put it back together to understand the whole rock behavior. Having a physics background where that’s not an unusual approach really helped.” 

First as a professor of materials science at Cornell University and then as a professor of earth sciences at the University of Minnesota, Kohlstedt and his team studied the roles of a small amount of melt and a small amount of water on the viscosity of mantle rocks. One important result from their research was the observation that the equivalent of oceans of water can stored as hydrogen ions in the vast expanse of Earth’s mantle. They are now examining questions surrounding the nature of the weak boundaries of tectonic plates. Their goal is to unravel how weak materials are created out of otherwise very strong rock, and how these plate boundaries remain weak for millions of years even at extreme pressures and temperatures. 

A major obstacle to understanding how the properties and behavior of rocks are affected by the heat and pressure of Earth’s mantle — at least at the scientific level — is the very slow rate at which phenomena such as convection occur. An observable change could be expected to take decades or centuries, clearly a challenge to study quantitatively. “Graduate students just aren’t willing to be around for 100 years to do those experiments and get their Ph.D.s,” Professor Kohlstedt jokes. Thus extrapolation of experimental results from laboratory to geological time scales is critical.

A second limiting factor is that, while specialized lab equipment can create temperatures and pressures that exceed those of Earth’s core in the lab, samples subjected to such extreme pressure have to be very small. “For our experiments at mantle pressures and temperatures, samples are the size of my little finger. Keep in mind that the results of the experiments must be applied to understanding processes occurring over hundreds of kilometers deep within our planet,” Professor Kohlstedt says, “so extrapolation in length scale is also essential.”

For his ‘pioneering experiments [that] have shown how processes at inaccessible depths drive what happens on the planet’s surface’ Professor Kohlstedt has earned one of the highest honors in earth science: the Vetlesen Prize. The $250,000 awarded the winners  will be shared among several charitable causes, perhaps also adding to  the endowments he and his wife have already established at the University of Minnesota and Valparaiso University to provide scholarship funds for students and research funds for physics faculty. “Having been a faculty member for some time, I appreciate just how difficult it can be to find money to travel or buy equipment,” Professor Kohlstedt says. 

For students and other young people looking to make their mark in their field, Professor Kohlstedt’s advice is straightforward. “Act boldly,” he says. “At times, I didn’t have a clear picture of what the next step was going to be. For example, when I went to MIT to do a postdoc in geophysics having never taken an earth science course in my life, I had no idea what lay ahead professionally. For me it was following my instinct and my curiosity, while hoping like heck that it would work out. That’s a key thing: if there’s something you enjoy doing, it’s really worth throwing yourself into the inquiry and following the sometimes unexpected results.”