The dark, high-pressure depths of Earth’s interior is an unexpected place to find life. Now, an international group of scientists report there’s 16.5 to 25 billion tons of micro-organisms beneath the planet’s surface. The team’s work is redefining what a habitable environment is.

The discoveries “force us to reimagine what the boundaries are that life can exist in,” said Karen Lloyd, a microbiologist at the University of Tennessee in Knoxville.

Deep Discovery

Lloyd is a member of the Deep Carbon Observatory (DCO), a collaborative network of more than 1,000 geologists, chemists, physicists and biologists around the globe that is uncovering the life buried within the Earth. The group is on a decade-long mission to discover how the carbon stored deep in the Earth affects life on the surface.

The collaboration has revealed that life teems beneath the planet’s surface in a vast ecosystem scientists call “the deep biosphere.” A diverse mix of environments make up this other world beneath Earth’s crust, which encompasses a volume nearly twice as large as all the oceans combined. And surprisingly, life flourishes there, the researchers announced today.

“Every time we look in one of these disparate environments, we find living things,” Lloyd said.

The scientists probed hundreds of locations around the globe. They drilled a mile and a half into the seafloor and excavated gold and diamond mines in South Africa. So far, the deepest specimens of life come from more than 3 miles beneath the surface.

The mass of life in this deep biosphere adds up to hundreds of times more than all of the humans on Earth, the researchers calculated, and most of it is microbes. About 70 percent of the world’s bacteria and their single-celled cousins, the archaea, inhabit the deep biosphere, the researchers found.