Beneath our feet, in sunless depths once thought barren, a vast and vibrant ecosystem thrives.

A groundbreaking study by Chinese and Canadian scientists has revealed the surprising “energy engine” powering this hidden biosphere: the very breaking and grinding of Earth’s crust during earthquakes and tectonic shifts.

Forget 19th century French novelist Jules Verne’s fantastical depictions of mastodons and giant dragonflies dwelling in mushroom forests nine to 12 metres (30 to 40 feet) tall in an illuminated subterranean world. Traditional science held that kilometres below the surface, cut off from sunlight and surface organics, life could not exist.

Yet, recent discoveries have unveiled a massive, active deep biosphere, harbouring an estimated 95 per cent of Earth’s prokaryotes and constituting roughly one-fifth of Earth’s total biomass.

But how do these microbes survive in the deepest, most isolated zones?

A study led by Zhu Jianxi and He Hongping, professors at the Guangzhou Institute of Geochemistry (GIG) under the Chinese Academy of Sciences, and Kurt Konhauser, professor at the University of Alberta, provides an answer.

Their findings were published in Science Advances on July 19.

They discovered that seismic activity and crustal fracturing act like a natural “generator”, constantly producing energy for deep life.

“In the silent darkness, chemical reactions between rock and water generate energy. This process functions like a battery, creating positive and negative poles that drive electron flow – the currency of life’s metabolism,” Zhu said in a GIG news release on July 19.

The team simulated Earth’s most common silicate mineral, quartz, in the lab to recreate two fundamental types of rock fracture: extension, where rocks suddenly crack open, exposing fresh surfaces instantly to water; and shear fracture, where faults grind continuously, crushing rocks in water.

Both fracture types split water molecules, producing hydrogen gas and reactive oxygen species. Extensions were particularly efficient at accumulating hydrogen peroxide.

The hydrogen peroxide paired with the generated hydrogen to form a natural “redox couple” – a pair of chemicals that drive reduction-oxidation reactions. This reaction produced electrical energy of up to 0.82 volts, easily sufficient to power most life-sustaining reactions.

Iron, one of Earth’s most abundant elements, acts as a crucial energy shuttle. Tiny amounts of hydrogen peroxide oxidise dissolved ferrous iron into ferric iron. Simultaneously, abundant reactive hydrogen atoms, produced during rock fracturing, reduce ferric iron minerals back to ferrous iron.

This continuous electron flow creates an “underground power grid”, energising microbial life and driving the biogeochemical cycles of carbon, nitrogen and sulphur.

As highlighted in the GIG report, the team discovered in 2023 that minerals under stress can produce oxygen at their surfaces, potentially exceeding production rates from atmospheric photochemistry.

“This long-overlooked radical chemistry could simultaneously explain the origins of Earth’s initial oxygen and hydrogen,” Zhu explained. “It might be the intrinsic mechanism driving the early co-evolution of minerals and life.”

“Furthermore, the deep subsurface provides a sanctuary, shielded from catastrophic events like intense ultraviolet radiation and asteroid impacts, offering a previously unrecognised crucial environment for the origin and evolution of life,” he added.

The study quantifies the power: a single moderate earthquake can generate hydrogen fluxes 100,000 times greater than production via radiolysis, which involves splitting water molecules through ionising radiation, or serpentinisation – a chemical reaction between water and ultramafic rocks at high temperatures and pressures.

Such intense energy flow can readily sustain populations of deep chemosynthetic microbes and may even lead to localised accumulations of dihydrogen gas.

According to He, “This process of converting mechanical energy into chemical energy isn’t unique to Earth.

“It applies to other planetary bodies like Mars … and Enceladus (a moon of the planet Saturn). Detecting signals related to redox couples – such as hydrogen, methane, oxygen, or redox fluctuations of iron – within Martian fault zones could indicate active subsurface life.”

So the next time you feel an earthquake’s tremor, remember: deep beneath the surface, in unfathomable darkness, shattering rocks might just be igniting sparks of life. The hidden worlds within Earth – and perhaps even Mars – could be far more alive than we ever imagined.