Excerpt from Becoming Earth by Ferris Jabr, plus links to reviews, author biography & more

The rail cars stopped. We stepped out and walked a short distance to a large plastic spigot protruding from the rock. A pearly stream of water trickled from the wall near the faucet's base, forming rivulets and pools. Hydrogen sulfide wafted from the water—the source of the chamber's odor. Kneeling, I realized that the water was teeming with a stringy white material similar to the skin of a poached egg. Caitlin Casar, a geobiologist, explained that the white fibers were microbes in the genus Thiothrix, which join together in long filaments and store sulfur in their cells, giving them a ghostly hue. Here we were, deep within Earth's crust—a place where, without human intervention, there would be no light and little oxygen—yet life was literally gushing from rock. This particular ecological hot spot had earned the nickname "Thiothrix Falls."

As I gingerly probed the strands of microbes with a pen, biogeochemist Brittany Kruger opened one of several valves on the spigot before us and began conducting various tests on the discharged fluid. By simply dribbling some of the water into a blue handheld device, reminiscent of a Star Trek tricorder, Kruger measured its pH, temperature, and dissolved solids. She clamped filters with extremely tiny pores onto some of the valves to collect any microorganisms drifting through the water. Meanwhile, Casar and environmental engineer Fabrizio Sabba examined a series of rock-filled cartridges that had been hooked up to the spigot. Back at the lab, they would analyze the contents to see if any microbes had flowed into the tubes and survived within them, despite the complete darkness, the lack of nutrients, and the absence of a breathable atmosphere.

On a different level of the mine, we sloshed through mud and shin-high water, stepping carefully to avoid tripping on submerged rails and stray stones. Here and there, delicate white crystals ornamented the ground and walls—most likely gypsum or calcite, the scientists told me. When our headlamps caught the tunnels of pitch-black rock at the right angle, the crystals shimmered like stars. After another twenty-minute journey, this time on foot, we reached another large spigot jutting out from the rock. Only half a mile underground, and better ventilated, this alcove was much cooler than the last. The rock around the faucet was mired in what looked like wet clay, which varied in color from pale salmon to brick red. This, too, Casar explained, was the work of microbes, in this case a genus known as Gallionella, which thrives in iron-rich waters and excretes twisted metal spires. At Casar's request, I filled a jug with fracture water from the faucet, scooped microbe-rich mud into plastic tubes, and stored them in coolers, where they would await future analysis.

Kruger and Casar have visited the former Homestake Mine at least twice a year for many years. Every time they return, they encounter enigmatic microbes that have never been successfully grown in a laboratory and species that have not yet been named. Their studies are part of a collaborative effort co-led by Magdalena Osburn, a professor at Northwestern University and a prominent member of the relatively new field known as geomicrobiology.

Osburn and her colleagues have shown that, contrary to long-held assumptions, Earth's interior is not barren. In fact, the majority of the planet's microbes—perhaps more than 90 percent—may live deep underground. These intraterrestrial microbes tend to be quite different from their counterparts on the surface. They are ancient and slow, reproducing infrequently and possibly living for millions of years. They often acquire energy in unusual ways, breathing rock instead of oxygen. And they seem capable of weathering geological cataclysms that would annihilate most creatures. Like the many tiny organisms in the ocean and atmosphere, the unique microbes within Earth's crust do not simply inhabit their surroundings—they transform them. Subsurface microbes carve vast caverns, concentrate minerals and precious metals, and regulate the global cycling of carbon and nutrients. Microbes may even have helped construct the continents, literally laying the groundwork for all other terrestrial life.

Excerpted from Becoming Earth by Ferris Jabr. Copyright © 2024 by Ferris Jabr. Excerpted by permission of Random House. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.