A biologist’s firsthand account of the hunt for life beneath earth’s surface—and how new discoveries are challenging our most basic assumptions about the nature of life on Earth

Life thrives in the deepest, darkest recesses of Earth’s crust—from methane seeps in the ocean floor to the highest reaches of Arctic permafrost—and it is unlike anything seen on the surface. Intraterrestrials shares what scientists are learning about these strange types of microbial life—and how research expeditions to some of the most extreme locales on the planet are broadening our understanding of what life is and how its earliest forms may have evolved.

Drawing on her experiences and those of her fellow scientists working in challenging and often dangerous conditions, Karen Lloyd takes readers on an adventure from the bottom of the ocean through the jungles of Central America to the high-altitude volcanoes of the Andes. Only discovered in recent decades, “intraterrestrials”—subsurface beings that are truly alien—are demonstrating how life can exist in boiling water, pure acid, and bleach. They enable us to peer back to the very dawn of life on Earth, disclosing deep branches on the tree of life that push the limits of what we thought possible. Some can “breathe” rocks or even electrons. Others may live for hundreds of thousands of years or longer. All of them are living in ways that are totally foreign to us surface dwellers.

Blending captivating storytelling with the latest science, Intraterrestrials reveals what microbes in Earth’s deep subsurface biosphere can tell us about the prospects for finding life on other planets—and the future of life on our own.

"Longlisted for the PEN/E.O. Wilson Literary Science Writing Award, PEN America"
"Lloyd is one of those rare gifted writers who can be as broadly profound as she is precise, able to make science both come raucously alive and resonate with meaning. She does this via perfect metaphors, an effortless wit, and a massively infectious enthusiasm for the outsize significance of her very small subjects. This science book is, furthermore, part adventure story, as she travels to the ends of the earth to pursue her small subjects, and generally bears witness to 'the shocking enormity of what we have been missing about life on Earth." * Kirkus Reviews, starred review *
"Lloyd, an environmental studies professor at the University of Southern California, debuts with an astonishing study of the remarkable microorganisms that thrive in the 'subsurface biosphere.' . . . Filled with mind-blowing trivia that will change how readers think about life on Earth, this captivates." * Publishers Weekly, starred review *
"At a beach-bag-friendly 200 pages or so, this lively and compulsively engaging book is an unusual page-turner. Lloyd, a geomicrobiologist, expertly guides readers who have a taste for biological adventures to ‘intraterrestrial’ life: microorganisms that survive under the most extreme environmental conditions, such as in Earth’s deep sediments, deep ocean crust, volcanoes and permafrost soil. . . . Thanks to Intraterrestrials, the general reader can now peek into the work of this network of experts and hopefully leave with a changed perspective as regards microbial life on and within this planet, and of its antiquity, evolutionary pace, adaptability and extraordinary tenacity."---Andreas Teske, Nature
"Intraterrestrials: Discovering the Strangest Life on Earth by Karen G. Lloyd is a much-needed field guide to Earth’s subterranean life. . . . Through witty prose, she brings us along on some of her own adventures chasing microbes from the high desert of the Andes to the perilous summit of a Costa Rican volcano. These are scenes out of an action movie: careful not to slip on the shards of volcanic glass, lest you fall into the lake of acid! . . . All this makes for fun and evocative reading about biogeochemistry."---James Dineen, New Scientist
"The author gives us a completely new appreciation of how deep life is embedded in our own planet."---Bruce Dorminey, Forbes
"[A] must-read."---Mark Martin, Matters Microbial
"Fascinating."---Brian Clegg, Popular Science
"[This] book is so fascinating."---Mia Funk, One Planet Podcast
"[Lloyd] manages to weave an interesting narrative that is provocative and compelling."---M. S. Field, Choice
"The central question Lloyd poses in her fascinating exploration of underground microbial ecology—are there life-forms hiding inside Earth that are so strange that they change our conception of life itself?—is easily answered. Yes!"---Tony Miksanek, Booklist
"Microbes live in permanent darkness, in environments with no oxygen, often surrounded by harsh conditions and pressures. How do they breathe? How do they eat? The answers will surprise and delight."---Brandy Schillace, Wall Street Journal

Karen G. Lloyd is the Wrigley Chair in Environmental Studies and Professor of Earth Sciences at the University of Southern California. Her work has appeared in leading publications such as Nature and Science.