Intraterrestrials: The Strangest Life on Earth
How organisms that live deep beneath Earth's surface are challenging basic assumptions about the nature of life
Karen Lloyd
University of Southern California
Sponsored by PSW Science Member Charles Clark
About the Lecture
The discovery of intraterrestrials – life buried deep within Earth’s crust – in the past few decades has revolutionized understanding of the kinds of life present on Earth. Many of these organisms are on deep evolutionary branches on the tree of life, and have functions and ways of living that challenge what is known about biology. One of the strangest things about them is that much of this vast subsurface ecosystem, which has more living microbial cells then the number of stars in the universe, seems to be living in a long-term suspended animation. They are living and breathing, but do not divide and make new cells for thousands or even hundreds of thousands of years because they lack the energy flow rates necessary to allow even a single cell division. This puts this life more in the realm of geology than biology, and studying it may lead to clues about what limits lifespan across all types of life on Earth.
Selected Reading & Media References
Lloyd, K.G. 2025. Intraterrestrials: Discovering the Strangest Life on Earth, Princeton University Press.
Lloyd, K.G., A.D. Steen. 2025. Defining ultra-slow-growing extremophilic microorganisms as Aeonophiles. Nature Microbiology. 10: 1555-1557.
Lloyd, K. G. 2020. Time as a microbial resource. Environmental Microbiology Reports. 13(1): 18-21.
About the Speaker
Karen G. Lloyd holds the Wrigley Chair in Environmental Studies and is Professor of Earth Sciences at the University of Southern California. Previously, she was a member of the faculty in the Department of Microbiology at the University of Tennessee, Knoxville.
Karen’s research focuses on the microbial biogeochemistry of the deep subsurface biosphere, including uncultured microorganisms in extreme environments such as deep oceanic sediments, hydrothermal vents, cold methane seeps, coastal estuaries, Arctic permafrost, and subduction zones. Her research integrates phylogenetic and functional data from RNA, DNA, proteins, and metabolites with geochemical parameters to understand carbon and energy sources, organic matter transformations, and the role of deep subsurface microbes in global processes such as methane cycling and their effects on climate.
Karen has done fieldwork in many locations to find and study these organisms, including the Arctic, Central and South America, the Baltic Sea, North Carolina estuaries, Siberia, and Mariana Trench seamounts. The work has advanced knowledge of methane-eating microbes’ role in sequestering greenhouse gases And it has revealed new microbial clades with ultra-slow metabolisms that can persist for thousands of years without reproducing. Understanding these organisms has led to the characterization of the “Aeonophiles” – ultra-slow-growing extremophiles, and has expanded understanding of evolutionary processes and the extremes of life’s limits.
Karen is an author on more than 100 peer-reviewed publications, along with several book chapters, and she is sole author of the book, Intraterrestrials: Discovering the Strangest Life on Earth which was longlisted for the PEN/EO Wilson Literary Award. She has delivered two TED Talks, appeared on numerous podcasts including Sean Carroll’s Mindscape and Coast to Canopy, and given many keynote addresses.
Among other honors and awards Karen has received a NASA Early Career Fellowship, a Simons Early Career Investigator award, an Alfred P. Sloan Research Fellowship, an NAS Kavli Fellowship, a U Tennessee Chancellor’s Award and Woods Hole Oceanographic Institution Holger Jannasch Award. She was also nominated for the UTK Blavatnik Award. And she won First Place in the Wild Orbit Film Festival in Paris.
Karen earned a BA in Biochemistry at Swarthmore College and an MSc and PhD in Marine Sciences at the University of North Carolina at Chapel Hill.
Social Media
Webpage(s): https://dornsife.usc.edu/lloyd/
LinkedIn Profile: https://www.linkedin.com/in/karen-lloyd-8b427250/
Bluesky: @karenlloyd.bsky.social
Instagram: @karenlloyd946