Cracked rocks power life deep on Earth - and possibly other planets

Deep underground, far from any ray of sunlight, microbes stay alive thanks to energy released when rocks crack. A new study traces that energy to hydrogen and oxidants created during fault movements, challenging the persistent view that “all life depends on sunlight.”

Lead investigators Professor He Hongping and Professor Zhu Jianxi at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIGCAS), used high-pressure experiments to mimic earthquakes.

The researchers watched free radicals tear water apart, producing hydrogen gas and hydrogen peroxide.

“Hydrogen production driven by earthquake-related faulting was up to 100,000 times greater than that from other known pathways,” said study first author Xiao Wu.

Cracks in rocks beat sunshine

Sunlight fades within a few yards of bedrock, yet the deep biosphere hosts roughly 15 percent of Earth’s biomass, mainly bacteria and archaea.

Two billion years of plate movements and daily microquakes keep that hidden ecosystem supplied with freshly fractured surfaces.

When quartz or basalt breaks, it creates reactive radicals that split water into hydrogen gas and peroxide – an energy source microbes can use.

Because the deep crust is full of silicate grains with hidden peroxy bonds, each seismic slip has a big effect. It’s like flipping millions of nanoscale switches at once.

Breaking those bonds converts about 0.005 percent of the mechanical energy into chemical energy. The authors argue that’s enough to keep underground microbes active between major quakes.

Microbes thrive on rock cracks

The team’s laboratory faults generated up to 160 micromoles of hydrogen in just four hours, dwarfing the yield from serpentinization or natural radiolysis under similar volumes.

Production hit 33.1 moles per square yard yearly – enough to sustain dense microbial biofilms, the authors say.

Such bursts matter because many subsurface cells scrape by on barely 10⁻¹² watts apiece, near the threshold estimated by astrobiologist Tori Hoehler for metabolic maintenance.

A single quake therefore provides millions of times the power one microbe needs, turning fresh rock cracks into temporary oases.

Seismologists have recorded hydrogen spikes in hot spring gas just hours before moderate quakes on the Tibetan Plateau. This highlights the strong connection between tectonic activity and underground chemistry.

Field evidence supports the lab results, showing tiny amounts of oxygen forming as hydrogen peroxide breaks down – even in the dark.

Rust fuels life below

Hydrogen alone is not enough; life also needs an electron acceptor. The experiments showed that reactive hydrogen atoms easily convert ferric iron (Fe³⁺) back into ferrous iron (Fe²⁺).

At the same time, hydrogen peroxide turns Fe²⁺ back into Fe³⁺ in nearby pores, creating a self-sustaining iron cycle. In nature, some bacteria use this iron exchange to get energy and support the carbon cycle.

Lab tests on granite showed that some microbes can grow by pulling electrons from iron in the rock. They turn the iron into rust, revealing how vital this process is for underground life.

Once established, the gradient persists as slow weathering and diffusive mixing blur the initial burst, giving communities time to stabilize and spread.

The study indicates that these self-renewing redox interfaces may dot fault networks worldwide, vastly enlarging habitable volume. Field samples from deep Canadian Shield boreholes show iron shifting between forms over several years.

This suggests underground microbes stay active by using hydrogen from fractured rock. Such evidence backs the lab findings that iron redox shuttles act as long-term batteries.

Hidden energy below ground

Global estimates say processes like radiolysis and serpentinization produce up to 18 billion moles of hydrogen each year.

Though earthquakes are rare, they release intense energy in small areas – enough to rival other sources and power surface-dwelling microbes.

Glaciers provide a similar example. As they grind up basalt rock beneath the ice, they release hydrogen that can support microbial life in the water below.

Together, these findings recast mechanical energy as a prime mover in parts of the biosphere once thought inert.

With countless microbes living underground, even rare quakes can recharge their energy and reshuffle communities until power runs out again.

When chemistry slows, some microbes go dormant and survive on tiny energy for thousands of years. This has been seen in deep South African gold mines, showing how adaptable underground life is.

Hints for life on other worlds

Rocky planets with brittle crusts experience fracturing from impacts, tides, and cooling, so similar chemistry could run beneath Mars, Europa, or Enceladus.

Mars orbiters have already mapped rock cracks in the surface that stretch for hundreds of miles, and rovers have found types of iron that can switch between two different forms.

Studies reviewing rock-hosted life on Earth argue that such interfaces, not surface oases, may offer the best hope of past or present Martian life.

Tools that detect hydrogen, methane, or changes in iron might spot signs of life – even in dry, barren landscapes. The new data give mission planners quantitative targets, narrowing the search to cracks in rocks where chemistry and biology intersect.

Back on Earth, the work broadens our picture of the deep biosphere, showing that tectonic stirrings, glacier creep, and landslide-grinding all seed underground food chains. Once again, life proves it can run its circuits wherever electrons find a path.

The study is published in the journal Science Advances.

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