‘Worms from hell’ 2 miles underground

PRINCETON (US) — On what he likes to call “underground safaris,” a geoscientist made a startling discovery: tiny worms living nearly two-and-a-half miles beneath the Earth’s surface.

This particular “extremophile”—an organism found in habitats considered uninhabitable—is remarkable not only for the depth at which it was found but also for its biological complexity.

These half-millimeter-long nematodes—roughly a quarter of the diameter of the head of a pin—can apparently tolerate very high temperatures, prompting the researchers to nickname them “worms from hell.” The worms also reproduce asexually and feed on bacteria from the subsurface. Tullis Onstott, the Princeton University professor who led the research, says, given their size, finding these nematodes at such depths was akin to “finding Moby Dick in Lake Ontario.”

Onstott’s research team, which he led with Gaetan Borgonie of the University of Ghent in Belgium, found the worms in several South African gold mines. Although nematode species have been known to live as far as 20 feet below the surface, scientists generally assumed there was no reason to believe the organisms would be found anywhere near the depths of those found by Onstott’s team.

The discovery, which was published recently in the journal Nature, raises questions about not only the possibility of even more complex organisms miles below the Earth’s surface, but also the likelihood of life far into space.

“The potential to look for alien life on other planets exists, in a way, right here on Earth,” says Onstott. “What we’re looking for are ‘extremophiles’ deep within the Earth, living in an environment that could also occur on other planets.”

Finding life forms in unexpected places appeals to the imagination, says Onstott. “It’s almost science fiction in that regard. The search for life in these strange environments itself is something that broadens human perspective on life, and that’s very important in helping us better understand how life evolves and how bizarre life can be.”

Dig deep
The last 15 years of Onstott’s subterranean work have taken him to myriad locales across the globe. Not only does he frequent the gold mines of South Africa—where temperatures often approach 95 very humid degrees—he has also taken several trips to the gold mines of Canada, where the warm air from the Earth’s depths collides so quickly with sub-freezing surface temperatures that “snowflakes the size of chandeliers” form inside the mine, he says.

This makes Onstott think of Mars, where the conditions match those of the Canadian mines quite remarkably in certain spots.

“Everything is frozen on the Martian surface, but you go down a half-kilometer or so and things get warmer,” says Onstott. “Also, you have caves on Mars where water might have risen through evaporation and frozen and crystalized. That’s where you want to go looking for life on Mars.”

More questions
Onstott is particularly excited to see how the discovery of these “worms from hell” further informs scientists’ understanding of this planet. For instance, Onstott wants to figure out what relationship these South African nematodes—dubbed Halicephalobus mephisto in honor of the sinister, darkness-loving demon Mephistopheles of literary lore—may have with subsurface radiation as a means of energy.

Onstott would also like to complete the gene sequence for H. mephisto and compare it to the genomes of closely related species found near the surface of the mines. This should give him a better sense of whether or not the nematode has adapted or evolved in the subsurface, and help him answer the pressing question of whether or not life can originate so far down, he says.

“We still don’t know how far down the biosphere goes,” Onstott says. “We have an expectation that it stops at a certain temperature, but we haven’t found that particular boundary yet. And if we do, the next question becomes: What lies beyond that?”

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