Microbes buried for millions of years may guide the search for alien life

There’s an entire world beneath our feet – ancient, resilient, and almost unimaginably strange. Over the past two decades, scientists have revealed that Earth’s crust is packed with a living biomass. The microbes persist for hundreds of thousands – even hundreds of millions – of years in places once deemed uninhabitable.

They tolerate boiling heat, extreme acidity, and bleach-like chemistry; some “breathe” metals; many exist at energy levels so low they barely scrape by. This is the realm geobiologist Karen Lloyd explores – a hidden biosphere that is forcing us to rethink what life is and how it endures.

Collecting microbes on the edge

Eight years ago, Lloyd stood on the rim of Costa Rica’s Poás Volcano, peering into a churning, acid-filled crater while collecting samples of deep groundwater brought to the surface by tectonic forces. The scene was otherworldly.

She turned to a local collaborator and asked, “What’s our exit strategy again if this thing goes off?” His answer – “Just turn around and admire the view. Because it’s going to be the last one you’ll ever see” – landed somewhere between gallows humor and practical advice.

Less than two months later, Poás erupted in Costa Rica’s most serious volcanic eruption in over 60 years. The samples survived – and so did the science.

Chasing microbes underground

Lloyd, a professor of Earth sciences at the University of Southern California, is part of a global effort that has made the subsurface biosphere impossible to ignore.

“Overcoming the challenges of sample contamination to find conclusive proof took years of painstaking work, but the evidence is now overwhelming,” Lloyd said.

“These deep-life microbes are real. They’re alive and they have decidedly weird lifestyles – doing strange, fascinating things we’re only just beginning to understand.”

Her field sites are natural windows into the deep. They include rift basins in the American Southwest that tug ancient fluids upward. She also studies volcanic hot zones in Iceland and New Zealand.

In addition, she works in subduction settings in Costa Rica and the Andes, where Earth wrings old groundwater toward the surface like a soaked cloth. Each locale presents a different chemistry – and a fresh chance to catch deep life in the act.

Time capsules in seafloor mud

Some of the most revealing clues come from beneath the ocean floor. Lloyd’s team uses drills, push cores, and submersibles to retrieve columns of mud, then slices them layer by layer to track how microbial life changes with depth and time.

“Imagine being one of those cells: you settle out of the water column with a slow rain of dead plankton and dust, get buried grain by grain, and then…wait. For millennia. For eons,” Lloyd said.

“And you keep living for all that time,” she said. “These are not lively lives. There’s not enough energy down there to reproduce. But they persist – barely – metabolizing just enough to survive.”

Genetically, these microbes are extraordinarily diverse – far more so than most visible creatures at the surface. Many lineages diverged billions of years ago, making the evolutionary distance between, say, a human and a jellyfish look like a weekend road trip by comparison.

Underground microbes that breathe metals

What sets subsurface life apart is how it gets energy. “Most visible life on Earth either respires oxygen, ferments, or photosynthesizes – and that’s it,” Lloyd explained.

“But some species of subsurface life can ‘breathe’ every metal on the periodic table, including arsenic, while others breathe carbon dioxide.”

In practice, “breathing” here means using redox reactions – electron exchanges – to power the cell, often without oxygen.

Remarkably, metal-breathing shows up across distantly related branches of the tree of life, a testament to how evolution finds similar solutions in very different bodies.

Big potential in tiny microbes

This isn’t just esoteric biology – the weirdness of deep life could translate into tools we need.

One of Lloyd’s collaborators, Andrew Steen, is studying whether protein-stabilizing tricks from these microbes might help vaccines remain potent without refrigeration, which could be transformative for global health.

In Costa Rica, Lloyd’s team also helped explain a nagging climate puzzle: why volcanoes emit huge plumes of CO₂ while hot springs in the same region release only trickles.

The culprit appears to be subsurface chemistry and microbes that convert CO₂ into carbonate minerals, locking carbon into rock before it escapes – an insight that could bolster carbon storage strategies.

In some conditions underground, microbes can even turn CO₂ into methane, a usable fuel (though one with climate trade-offs).

A new field of geobiochemistry

For Lloyd, the point isn’t to chase products – it’s to push the frontier. “I’m not looking for any particular solution or benefit,” she said. “My goal is to push the boundaries of what we know to best provide for other people who are doing practical stuff. That’s the promise of blue-sky research.”

Still, the horizon looks promising. “If we can make such a big breakthrough from just one study, then imagine what else is waiting to be discovered down there,” Lloyd said.

“This new field of geobiochemistry is going to have huge implications – maybe even predicting earthquakes or finding life beyond our planet.”

Clues for finding alien life

The subsurface biosphere reframes our assumptions about life’s requirements: abundant energy, fast growth, sunlight.

The underground microbes suggests another path – slow metabolism, fierce patience, astonishing adaptability. It opens new chapters in our understanding of evolution, the carbon cycle, and the possible habitats of life on other worlds where energy is scarce and time is long.

“Life buried deep within Earth’s crust may seem irrelevant to our daily lives,” said Lloyd. “But this weird, slow life may hold the answers to some of our planet’s greatest mysteries – and challenges.”

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