There's a 'Subterranean Galapagos' Deep Inside the Earth

There is a vast biosphere deep underground that is nearly twice as big as Earth’s oceans and contains some 23 billion tons of organisms.

This “subterranean Galapagos” was described on Monday by the Deep Carbon Observatory (DCO), a collaboration between 1,000 scientists studying “deep Earth” ecosystems, to kick off the American Geophysical Union’s annual meeting this week. According to researchers, knowing how organisms survive in the extreme conditions below Earth’s surface will help us understand the origins and evolution of life on our planet—and perhaps others.

“A decade ago, we had no idea that the rocks beneath our feet could be so vastly inhabited,” Isabelle Daniel, a mineralogist at Claude Bernard University Lyon 1 in France, said in a statement. “This is simply fascinating and will surely foster enthusiasm to look for the biotic-abiotic fringe on Earth and elsewhere.”

These “intraterrestrials” are microbes that can live miles beneath land and seafloor habitats. Though an estimated 70 percent of all bacteria and archaea on Earth live in this subsurface environment, very little is known about them because their habitats are so difficult for humans to access.

The DCO sampled hundreds of deep Earth habitats, sometimes drilling boreholes three miles deep to reach them. Millions of microbe species are estimated to occupy this biosphere, and some are able to survive boiling temperatures or pressures 400 times those at sea level. Many organisms take much more time to grow and reproduce compared to their counterparts on land because they subsist on fewer nutrients.

Species highlighted by the team include a nematode found a mile underground in the Kopanang gold mine of South Africa, a methane-breathing microbe discovered in a mile-deep borehole on the Pacific Ocean seafloor, and an archaea species in a sulfur-rich sample taken 100 feet below a hot spring in Germany.

It’s mind-boggling to imagine such a diverse biosphere existing beneath the ground we tread on, and it could have major implications for speculating about alien life on other worlds.

“Even in dark and energetically challenging conditions, intraterrestrial ecosystems have uniquely evolved and persisted over millions of years,” said Fumio Inagaki, a geomicrobiologist at the Japan Agency for Marine-Earth Science and Technology, in a DCO statement.

“Expanding our knowledge of deep life will inspire new insights into planetary habitability, leading us to understand why life emerged on our planet and whether life persists in the Martian subsurface and other celestial bodies.”

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