A Massive Underground World Houses "Ancient Cousins We Never Knew Existed"

Scientists find a "new type of ecosystem on Earth that was literally right under our noses."

Earth teems with life: It’s home to approximately 7.7 billion humans. There are a billion dogs, 10 billion bats, and around 200 billion birds. While it may seem that we’re all already sharing a crowded space, a new study reveals the tremendous amount of life existing far beyond what we can see.

On Monday, at the annual fall meeting of the American Geophysical Union, scientists presented the culmination of ten years of research on the microorganisms living beneath the surface of the Earth. The evidence suggests that the “deep biosphere” contains a total carbon mass of 15 to 23 billion tons of microorganisms. And they say they’ve only scratched the surface.

That’s hundreds of times the combined weight of each human on the planet. The findings, which span multiple papers, also state that 70 percent of all of Earth’s bacteria and archaea live underground.

“These organisms have likely been on Earth operating for billions of years and driving many of Earth’s geochemical systems that have led to the habitable world we now enjoy,” Karen Lloyd, Ph.D. tells Inverse. “It’s thrilling to play a small part of the discovery of a new type of ecosystem on Earth that was literally right under our noses.”

eukaryote
An unidentified nematode (eukaryote) found in an South African goldmine.

Lloyd, an associate professor of microbiology at the University of Tennessee in Knoxville, took part in some of the research and helped present the work. She and her colleagues are part of the Deep Carbon Observatory, a global research program dedicated to understanding the role of carbon on Earth. For the past decade, 1,200 scientists from 52 countries have searched for subterranean life by drilling into the seafloor and exploring the deep tunnels linked to mines. All of their findings suggest that genetic life is more diverse under the surface — not above it.

Bacteria and archaea are the groups of microbes most often found in the so-called “Deep Earth.” These strange organisms have evolved unique ways to survive. For example, Candidatus Desulforudis audaxviator is a species of bacteria that survives on hydrogen, discovered in a fluid and gas-filled fracture near a mine in Johannesburg, South Africa. The species Methanobacterium, meanwhile, produces and survives off methane, living in a coal bed beneath the Pacific Ocean floor of the coast of Japan.

Some of the microorganisms the team has discovered are thousands of years old. Nobody’s really sure how they managed to live that long.

“One thing that certainly helps is living in a place with very few disturbances,” Lloyd explains. “Surface microbial life is constantly struggling to claw back from a rain event washing everything away, or an amoeba decimating the population.”

“The deep subsurface microbes buried in marine sediment never has to deal with this — all they have to do is figure out how to seek out the last little bit of energy from the last bit of food available.”

methane
A species of *Methanobacterium*, which produces methane.

But most of the life in the deep biosphere — which the scientists say compares to the Galapagos or the Amazon in diversity — is still a mystery. These phantom organisms are referred to as “dark matter” — an Earthly version comparable to dark matter of space. Life has been found under the continental surface to a record depth of three miles, and six miles under the seafloor.

Lloyd and her colleagues still plan to “continue our downward trajectory to discover the absolute deep limits of life,” a journey they hope will reveal how these organisms can be useful to human society and how they evolved to live so far below.

“I find it wild that every time we dig down we find microbes that are on deep branches of the tree of life that have never been characterized in a laboratory,” Lloyd says. “These are like the ancient cousins that we never knew existed.”