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.

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.