Alumna Linda Kah’s “Rocky” Path, from Ancient Earth to Mars
Linda Kah is an expert on sedimentary rocks and ancient life, both on Earth and on Mars. Photo illustration by Gretchen Neff Lambert; photo courtesy of University of Tennessee, Knoxville
Linda Kah ’90, SM ’90 has never met a rock she didn’t like—a predilection she acquired early in life. When she was 5, she told her kindergarten teacher that she was either going to be a geologist, an archaeologist, or a truck driver. She stuck with option number one, and Kah is now an expert on sedimentary rocks and ancient life at the University of Tennessee, Knoxville, where she’s the Kenneth R. Walker Professor of Earth, Environmental, and Planetary Sciences.
As a child growing up in northern Ohio, she and her brother had fun unearthing the “treasures”—rocks, minerals, and fossils—they found in an old chest left behind by their grandfather. By the time she began undergraduate studies at MIT in 1986, she was intent on studying earth sciences—despite her father’s urgings to pursue physics, which he deemed “more broadly applicable.”
When Kah was a junior, the geologist John Grotzinger joined MIT’s faculty, and Kah recalls, “I found what I would spend the rest of my life doing.” Grotzinger’s specialty was a class of sedimentary rocks called carbonates (limestone is an example). Kah had long been intrigued by these rocks because she’s interested in the beginnings of life on Earth, and carbonates largely consist of tiny fragments of skeletons and shells. “These rocks give you a snapshot of Earth—its oceans and atmosphere—at the time they were formed,” she says.
These rocks give you a snapshot of Earth—its oceans and atmosphere—at the time they were formed.
Grotzinger introduced Kah to the geologist Andrew Knoll—an authority on the evolution of life—who became her advisor when she earned her PhD in geology at Harvard. Knoll studied rocks that formed about 530 million years ago, just before multicellular life first appeared on Earth, while Grotzinger studied rocks that were roughly 2.5 billion years old. Kah decided to work in the middle, focusing on a stretch of time labeled the Mesoproterozoic era.
“Several papers called it the dullest period in Earth’s history, ‘the boring billion,’ but it was only declared boring because there wasn’t any data,” Kah says. “It’s easy to say nothing’s going on in an area where nobody’s bothered to look.” Her research—carried out in remote places like the Canadian Arctic’s Baffin Island—has indicated that Earth actually underwent a major transition during the Mesoproterozoic era. Continents shifted, and sexual reproduction emerged in eukaryotic and multicellular organisms.
Working in remote areas made Kah well prepared for an opportunity that emerged in 2004. She was asked to participate in the Mars Science Laboratory—a NASA mission to use the Curiosity rover to explore the Red Planet, which has now been exploring Mars since 2012. At the time, she’d barely given planetary science any thought, “but when you get offered a ride that’s so amazing, you have to take it,” she says.
Kah has been studying Mars through its rocks ever since, and she’s presently engaged in both NASA’s Curiosity and Perseverance rover missions. In a paper published in Nature in September 2025, she and other scientists reported on a possible sign of early life on Mars: Martian rocks mottled with spots that indicate closely spaced oxidation-reduction changes. “Things like this are common on Earth rocks,” she says, where similar spots can be a byproduct of biological activity.
The Martian rocks, unfortunately, are still on Mars, which means Kah has no near-term prospect of inspecting actual samples. “A lot more needs to be done to demonstrate that this is a true marker of biological metabolisms,” she acknowledges.
In the meantime, there are plenty of fundamental questions regarding the origins of life on our own planet to keep her occupied. The answers, she suspects, may lie buried, deep within rocks.
