The dark high-pressure depths of the earth's interior are an unexpected place to find life. Now an international group of researchers reports that there are 16.5 to 25 billion tons of microorganisms below the surface of the planet. The team's work is redefining what a habitable environment is.
The discovery "forces us to rediscover the boundaries that life can exist in," says Karen Lloyd, a microbiologist at the University of Tennessee in Knoxville.
Lloyd is a member of the Deep Carbon Observatory (DCO), a collaboration network of more than 1,000 geologists, chemists, physicists and biologists all over the globe, revealing life buried in the Earth. The group is on a ten-year long mission to discover how the hydrocarbons are stored deep in the earth affects life on the surface.
The collaboration has revealed that life is below the surface of the planet in a large ecosystem researcher called "the deep biosphere." A diverse mix of environments constitutes this second world under the Earth's crust, which includes a volume that is almost twice as large as all the oceans combined. And surprisingly, life is blooming there, researchers told today.
"Every time we look in one of these different environments, we find living things," said Lloyd.
The researchers surveyed hundreds of places around the world. They drilled one and a half in the seabed and excavated gold and diamond mines in South Africa. So far, the deepest specimens of life come from more than 3 miles below the surface.
The mass of life in this deep biosphere adds up to hundreds of times more than all people on Earth, the researchers have calculated, and most are microbes. About 70 percent of the world's bacteria and their single cousins, the arches, are in the deep biosphere, researchers found.
Much of life researchers found under the surface of the earth are unlike what grows over. The masses of microorganisms in the deep biosphere are as extreme as the environment they inhabit. Some microbes researchers discovered can survive in temperatures up to 251 degrees Fahrenheit for example.
"It's far above the boiling point of the water," said Lloyd. "In our minds, we think it should be the upper limit of what life can do, but it certainly is not."
Life in the depths has adapted to other unthinkable ways for its environment. Food is scarce in a world where almost nothing happens. When scientists estimated how much energy the ecosystem uses, they found the organisms that can survive on virtually nothing at all.
"It's less than we thought would be able to support life," said Lloyd.
The team's results – published in the last nine years – will culminate in a final report that will expire next year. The discovery will help researchers explore the potential of the extraterrestrial life, researchers say.