Dr. Rondi Davies came to the American Museum of Natural History in 2002, where she is a postdoctoral research scientist in the Department of Earth and Planetary Sciences. Rondi grew up in Papua New Guinea until she was 11, where her father worked as a geologist. The family then moved back to her native Australia and she attended high school in Canberra.
“Growing up in Papua New Guinea was really great,” Rondi recalls. “It was in the tropics, we were outdoors all the time, we didn’t have television, and we swam constantly. Everything centered around the ocean.” Weekends found the family out on their boat, and Rondi and her three siblings were competitive swimmers who would fly around the country to swim meets “because there were no roads between towns, so you have to fly everywhere,” she explains. Vacations involved expeditions to places accessible only by helicopter, where they’d collect fish fossils and walk into steaming, sulfurous volcanoes.
In Canberra, the Davies family still spent lots of time outdoors. They skied, and Rondi continued to explore the natural world. A favorite pastime was going bush-walking (“hiking” in American). An inspirational outdoor education teacher took groups of students climbing, hiking, and caving almost every weekend. “Being challenged like this was a great way to become self-sufficient in the bush and to form trusting friendships. That’s when I decided to find a career doing something where I could be connected with nature,” she says. It was that love that led Rondi to take a geology course in her first year at the University of Sydney in Australia. She ended up majoring in the subject, which she enthusiastically compares to learning a new language. "Once you understand the terms and concepts, it's like opening a door to understanding the events that have created the foundations of our natural environment."
A high point of Rondi’s undergraduate work was a project in New Caledonia, an island about the size of New Jersey in the South Pacific east of Australia where “they have the most gorgeous rocks!” She was one of four geology students who camped out on a remote part of the island for six weeks, walking over hills, making colorful maps of the different rock types, and collecting samples. The rocks in this young and tectonically active region offer direct evidence of subduction processes. “They’re interesting because they’ve been subducted about 50 kilometers into the Earth and have come back up really fast, so they record unique high-pressure, low-temperature conditions that we don’t often see” Rondi explains. She’d signed up for the trip because studying these metamorphic, crystalline rocks was her favorite aspect of geology “because they tell stories. They’re rocks that record the events of their evolution, all the different geological episodes that they’ve experienced through time. It’s like a puzzle. You can unravel how they formed using many different techniques and observations.”
Every mineral grows under particular chemical and physical conditions (such as pressure and temperature) that are reflected in its composition and textures. “For example, if the minerals are all stretched in a certain way, it shows how they were compressed,” says Rondi. “And you can learn about how they came to Earth’s surface, their uplift history, because of ‘overprinting’ events — new minerals form that might overgrow the old ones, and new textures appear.”
This interest in high-pressure minerals led her to doctorate and postdoctorate research in the study of diamonds at Sydney's Macquarie University. Diamonds provide geologists with a unique opportunity to investigate the nature of the deep mantle where they crystallize, which helps them understand the intimate workings of the interior of the Earth. Because of their great hardness and low reactivity, diamonds and the impurities trapped inside them retain their original compositions without interacting with their changing environment. “They’re the only mineral that can form 700 km deep in the Earth and be transported to the surface where we can get hold of them and see what happened in the process,” Rondi explains.
Because a ton of a rare type of volcanic rock typically yields only a few carats of diamonds, Rondi doesn’t do the digging, and usually gets her samples from exploration companies that want to understand where the diamonds have come from. Her work takes place in the lab, where she observes and analyzes the mineral, “whatever I can do to the diamond, I do,” as she puts it — in a process that usually ends up reducing it to rubble. This can involve measuring the nature of nitrogen impurities in a diamond, which identify the conditions under which it was stored in the mantle, sometimes for billions of years. Some of the diamond may be burned to measure its carbon isotope composition in order to determine the origin of the carbon that makes the diamond. She also removes the minerals that were trapped inside the diamond as it was growing, which shed light on the composition of the mantle in which it formed. “You can get a lot of information from these tiny mineral inclusions,” she points out.
Rondi moved to New York to pursue this research at the American Museum of Natural History, and finds city life a lot of fun. A favorite haunt is Central Park, where she recently completed her second New York City marathon. Currently she has a Museum postdoctoral fellowship to study minerals that form in the mantle transition zone, between 410 and 670 km deep. “We don’t know very much about what’s down there. We only have models and experimental data to work from,” she explains. “In recent years, we’ve started to recognize that diamonds form that deep and we’re seeing minerals in diamonds that tell us about that area of the mantle. But we still have lots of questions.” To do this work Rondi goes into the laboratory and makes use of high-pressure and high-temperature experiments to probe the deep Earth while allowing for control of important system variables. “These experiments in the laboratory have allowed me to recreate the chemistry observed in deep diamond inclusions, thus yielding a more detailed understanding of connections between diamond characteristics and the environment of their formation.”
Her position also involves contributing to the Museum's educational outreach, an aspect she loves because, “the Museum is an amazing place, and I love to share my knowledge and passion for my work with others. I hope that it sparks people’s curiosity and transforms their perspectives of the planet.” Rondi found working on the Oceans course to be a wonderful challenge, “especially learning about how amazing water is — that can’t be overemphasized.” It’s her hope that people will take away a sense of how much more there is to learn about the ocean and what an interesting field ocean system science can be. “It’s really taking off,” she observes. “People are realizing the importance of the connections between all the spheres and at every level.”