The Alien Life Beneath Our Feet: An Interview with Microbial Biogeochemist Karen Lloyd

The search for extraterrestrial life often focuses on distant planets and galaxies, but fascinatingly alien organisms already exist right here on Earth. These microbes thrive in extreme environments like volcanoes, deep-sea hydrothermal vents, and Arctic permafrost, challenging our fundamental understanding of biology. In her new book, Intraterrestrials: Discovering the Strangest Life on Earth, microbial biogeochemist Karen Lloyd of the University of Southern California takes readers on a journey into this hidden world, exploring the unique adaptations and enduring mysteries of these “intraterrestrials.”

In a recent interview, Lloyd discussed the discoveries scientists have made about these organisms, the unanswered questions that remain, and the importance of studying life in Earth’s most extreme environments.

From Chemistry to the Deep Sea: A Serendipitous Path

Lloyd’s journey into the world of microbial biogeochemistry began with a fascination for chemistry. As an undergraduate student, she was drawn to the mysteriousness of the subject. However, she felt that chemistry grad school would be too narrow of a focus. She yearned to apply her knowledge in a more natural setting. This desire led her to oceanography, a field that embraces multiple disciplines.

"I chose oceanography so that I wouldn’t have to choose between biology, physics, chemistry, and geology," Lloyd explained. "I have to do them all."

A stroke of luck led her to a lab studying microbes isolated from the deep sea. Lloyd was unaware of the hidden world of deep life, but upon discovering it, she knew she had found her niche. This was a place where she could use her diverse scientific background to make new discoveries about biology. From that moment on, she was hooked.

Earthly Aliens: A Different Branch of the Tree of Life

What makes these subsurface life forms so strange and fascinating? Lloyd emphasized their evolutionary distance from familiar organisms.

"One of the biggest things that immediately jumps out at you is that these things are on deep branches on the tree of life," she stated. "So we might think that a slug is on a very different branch of the tree of life from like a kitty cat. But we’re talking about the slug and the kitty cat collapsing into the same branch compared to all these new types of microbes."

The genetic diversity of these microbes is astounding. They represent lineages of life that are vastly different from anything we encounter in our everyday experiences. This challenges our preconceived notions about the limits of life and reveals the incredible variety of life forms that exist on Earth.

Rewriting the Rules of Life: Ecosystems Without Sunlight or Oxygen

These subsurface microbes are not only different, but they also challenge established biological principles. Lloyd explained that while life without oxygen is not a new concept (e.g., bacteria in our guts), the discovery of entire ecosystems that function independently of oxygen and plant matter is revolutionary.

"The idea that you can have an entire ecosystem that never needs oxygen and never needs the influence of plant matter, for instance; that can basically just exist solely on chemical reactions coming from inside the Earth—that’s new," she stated. "That’s what we’re learning with these guys."

These ecosystems rely on chemosynthesis, where microbes derive energy from chemical reactions involving inorganic compounds like sulfur, iron, or methane. This discovery has broadened our understanding of the possibilities for life and highlights the potential for life to exist in other extreme environments, both on Earth and beyond.

Unanswered Questions: Exploring the Unknown

Despite significant progress, many fundamental questions about these subsurface microbes remain unanswered. Lloyd emphasized that much of what we know is inferred from specialized techniques, making it difficult to study these organisms in their natural environment.

"The biggest questions left are still very basic fundamental questions," she said. "You know, it’s not real. You can’t just walk up to them like you can a tree and be like, ‘Okay, that’s got roots. I know what it’s doing.’"

Key questions include: Who all is present in these ecosystems? What are they doing? What are they eating? What role do they play in the Earth’s processes, such as metal cycling and geological evolution? Understanding the interactions between these microbes and their environment is crucial for unraveling the mysteries of deep life.

Exploring Subduction Zones: A New Zealand Adventure

Lloyd’s current research focuses on subduction zones, where tectonic plates collide. These zones create unique environments, fostering subsurface microbial communities. Recently, she returned from a research trip to New Zealand.

"They have an amazing subduction zone," she explained. "That’s where two tectonic plates are overlapping each other. And that process creates volcanoes, but it also creates this sort of like alchemic mixture that enables these subsurface communities to take hold."

The research involved sampling diverse terrestrial environments in New Zealand and collaborating with local scientists. This collaborative and exploratory aspect of the work adds to the excitement and impact of studying these hidden ecosystems.

A Message of Hope and Possibility: Discovering the Unknown

Lloyd hopes that readers of her book will come away with a sense of hope and possibility about scientific discovery. In a world where it can feel like all the major questions have been answered, she emphasizes that there is still much to explore.

"I hope that people feel a sense of hope and possibility," she said. "One can imagine that you could get stuck thinking that all science is known or that the questions are small because we’ve tackled all the big ones. That there’s nothing left to explore."

Lloyd urges readers to recognize that our understanding of life is constantly evolving. The discovery of these "intraterrestrials" highlights the vast unknown that lies beneath our feet.

"There’s a whole world underneath our feet, for example," she concludes. "Not that there aren’t mysteries in those other places too, but we are just tapping into this stuff. So I hope that people leave with a sense of hope and possibility at all the amazing things we have left to learn about life here."