A biologist’s firsthand account of encounters with the planet’s most bizarre organisms—and how these discoveries are challenging our most basic assumptions about 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.

"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)