There's a vast and untouched ecosystem bristling with lifeforms that have never seen the light of day. It's bigger than all of the Earth's oceans. And it's beneath our very feet.
That's the startling conclusion of a 10-year study by 1,200 scientists from around the world after probing miles into the Earth's subsurface — and finding a brave new world buried deep within the one we know.
"It's like finding a whole new reservoir of life on Earth," Karen Lloyd, a professor at the University of Tennessee in Knoxville, tells The Guardian. "We are discovering new types of life all the time. So much of life is within the Earth rather than on top of it."
In all, researchers estimate the subsurface hosts anywhere from 15 billion to 23 billion tons of microorganisms. That's several hundred times more than all the mass of every human on the planet put together.
What lies beneath
You might forgive scientists for long overlooking the world beneath our feet. After all, at those depths, there's no light and only trace amounts of nutrition. Then there's the extreme heat and crushing pressure.
How could life thrive in those suffocating depths? Well, it depends on what we're looking for. The denizens of the subsurface aren't your garden variety life forms.
Take the barbed Altiarchaeales, for example. Oft-referred to as "microbial dark matter," these single-celled organisms, like bacteria, don't have a nucleus, but rather just a single chromosome. Nonetheless, they're crucial players on the microbial stage — found at the bottom of the sea amid hydrothermal vents that reach a piping hot 121 degrees Celsius.
In fact, the researchers note, 70 percent of the planet's bacteria and archaea call the subsurface home. Another kind of archaea just now making itself known to surface dwellers is the methanogen, a microorganism that manages to create methane out of nearly nothing at all.
"The strangest thing for me is that some organisms can exist for millennia. They are metabolically active but in stasis, with less energy than we thought possible of supporting life," Lloyd told The Guardian.
The research was conducted by the Deep Carbon Observatory, a global research initiative founded in 2009 with the aim of investigating "how the deep carbon cycle drives our world."
Scientists were helped by new drills that could bore deeper than ever into the planet's crust, as well as high-powered microscopes with Hubble-like ability to peer deeply into these subterranean biospheres.
In a press release, scientists referred to the subsurface as a "subterranean Galapagos" for the dizzying diversity of life it hosts.
And if all that microbial life sounds alien to you, that may just be the point of the research: to expand our parameters for defining life. And in doing so, perhaps, make it easier to find life beyond this planet.
"We must ask ourselves: if life on Earth can be this different from what experience has led us to expect, then what strangeness might await as we probe for life on other worlds?" muses mineralogist Robert Hazen in The Guardian.
Indeed, we may find planets teeming with life — once our own planet teaches us what to look for.