As she entered graduate school at Arizona State University in the mid-2000s studying geosciences, Erin DiMaggio had her sights on Mars. It was an exciting time for discovery as NASA’s Spirit and Opportunity rovers combed the red planet searching for signs of water.
But she also knew she loved doing fieldwork. And Mars, literally and figuratively, seemed so far away.
Instead, she jumped on an opportunity to take a summer field course in Kenya, which led to research alongside archeologists and anthropologists in Ethiopia. Both regions are famous for discoveries that have helped write the story of human origins.
DiMaggio, an associate research professor in the Department of Geosciences, works in the Afar region of Ethiopia, where the earliest fossils of our genus Homo were discovered. It’s also where the famed Australopithecus “Lucy” was found in 1974.
Earlier this year, DiMaggio’s team—the Ledi-Geraru Research Project out of Arizona State University—found strong evidence in the form of fossilized teeth indicating that early Homo and Australopithecus co-existed in the Afar region around 2.6 million years ago. That discovery suggests a less-than-linear evolutionary pathway to modern humans.
In 2019, DiMaggio began work in Kenya with the Southern Kenya Research Project on a fossiliferous region that dates to around six million years ago. This is an important time when human and chimpanzee lineages are thought to have split from an ape ancestor, marking the very beginning of our story.
These sites in Kenya and Ethiopia represent less well studied periods of early human evolution,” DiMaggio said. “Hominin fossil discoveries are rare but tremendously exciting—even the smallest teeth have a story to tell. As geologists, we think about the stories the rocks tell us. What was the environment like in eastern Africa at the dawn of our lineage? Humans were intimately tied to their surroundings—think of food sources or shelter. We study paleoenvironments and how they changed to learn about the conditions under which we evolved.”
From field to the lab
For the past two decades, DiMaggio has conducted field work with international and multidisciplinary teams of researchers. They spend weeks camping in remote places, and with the help of local friends and colleagues they carefully collect data, often under intense heat and in dusty conditions.
Her role is to map and document the rocks and determine the age of the rock layers. Because the regions are volcanically active, DiMaggio and her team can radiometrically date ash they find in the ancient rock layers. In a lab in the Deike Building at University Park, these ash samples are processed, and minerals and volcanic glass are carefully isolated for analysis.
“The fossils themselves can’t be dated because they are too old,” DiMaggio said. “Instead, we date ash layers near the fossil beds.”
But geology can be messy. Rocks can move up or down through time by faulting–cracks in the rock layers–and this complicates the whole picture. That’s why field work is important, DiMaggio said.
“We are continuously revising the geology maps, and especially now with the help of drones for high resolution topography and imagery,” she said.
Assisted by students
Back in the lab at Penn State, Millennium Scholar, Saia Pride takes pictures of volcanic ash and Bella Sullivan and Evelyn Atkins prep samples from sites in Kenya gathered by Abby Mensch, who visited the region before graduating in 2023 with her bachelor’s degree in geosciences from Penn State.
Mensch is one of many undergraduate students —like Pride and Atkins—in the Department of Geosciences who have worked with DiMaggio in the field and lab to gain hands-on research experience.
Sullivan, a master’s degree student advised by DiMaggio, sieves samples from two locations in Kenya. She is looking for minerals like feldspar that formed in the magma chamber before the volcano erupted, and glass shards or pumice that formed when magma quickly cooled during the eruption.
“They also should match physically,” Sullivan said, as she discussed the process for linking ash from the same eruption, a key part of her thesis project. “We need to confirm they are compositionally the same, even though the ages match.”
An interdisciplinary approach
Sullivan said the concept of working with paleontologists and archeologists on something as important as the geology of early human evolution drove her to the project.
That’s also what enticed DiMaggio when she began working in Africa twenty years ago.
“It’s special to know your work contributes to questions as basic as understanding when and how we evolved,” DiMaggio said. “And, combined with exceptional colleagues, it’s motivating!”
Millions of years of geological activity have preserved clues in the fossils and rocks now eroding from hillslopes in eastern Africa. Each discovery, each new date, refines our understanding of how we became us.
The answers lie in the rock, waiting to be uncovered.