In 2009, researchers discovered a tiny nematode living happily in the water inside rock fractures, more than a kilometer deep in a South African goldmine. They nicknamed the new creature the “devil worm” in honor of its dark, hot, deep home. Ever since the discovery of this and similar animals found more than three kilometers deep, they have wondered, how did these creatures get there?
In a new paper  in Scientific Reports, the researchers finally reveal the answer. By collecting water samples from boreholes in several South African mines and simulating the effects of earthquakes, the researchers propose that seismic activity forces surface water, and any organisms it contains, into deeper, rocky environments. While many of the imported organisms likely die off, some survive and reproduce. The findings suggest that areas with significant seismic activity may be good places to dig when looking for life on Mars because these sites may harbor life forms that once thrived on the surface. DCO members Gaetan Borgonie (Extreme Life Isyensya, Belgium), Cara Magnabosco (Flatiron Institute, USA), Borja Linage-Alvarez (University of the Free State, South Africa), Esta van Heerden (BioSaense Solutions, South Africa), Barbara Sherwood Lollar (University of Toronto, Canada), and Tullis Onstott (Princeton University, USA), collaborated on the project along with Scott Mundle (University of Windsor, Canada).
While Borgonie has spent decades studying microscopic worms, like nematodes and flatworms, he also has nurtured a long fascination with the potential for life on Mars. “My biggest dream is to go to Mars,” said Borgonie, “though I don’t think Elon Musk will think of me.”
Borgonie decided to combine his two interests and in 2009 travelled to South Africa with Onstott to collect water samples from exploratory boreholes drilled deep within gold, platinum, and diamond mines. He wanted to know if microscopic worms lived in Earth’s subsurface, to see if the subsurface on Mars might also support life. During this expedition, they discovered the devil worm, as well as other nematodes, some algae species and three insects, one of which was a diving beetle. The majority of the animals appeared to be surface freshwater species.
Since the organisms did not seem to be tunneling down from the soil, the researchers looked into the frequent seismic activity in the region as a possible explanation. South Africa has a long history of earthquakes, and mining activities contribute to their frequency. The researchers suspected that earthquakes create fractures in rock that allow surface water to rush into the cracks. When they examined fracture maps for the two mines in the current study, they saw that the fault lines connect nearby rivers to the boreholes.
The researchers collected water samples from boreholes in Kopanang gold mine (1.4 kilometers deep) and Zondereinde platinum mine (1.7 kilometers deep) and sediment samples from the two nearby rivers. They filtered out any small organisms and analyzed DNA from the samples to look for signs of bacteria, protists, and animals. The Zondereinde mine had no detectable protists or animals, possibly because they were unable to sample sufficient volumes of water, or because the water was too hot. They did collect nematodes from the Kopanang mine, however, which based on DNA analysis, appear to be the same species of worm living in the nearby Vaal river. “When we put them together to mate they reproduced, which means that they are the same species,” said Borgonie.
The researchers also simulated seismic activity by closing off a borehole so that the water pressure would build, then opening it suddenly to simulate the opening of a new fracture. They recorded the event with a camera, which revealed sediment, bits of bacterial biofilm, and bubbles rushing through the borehole when the pressure dropped.
The nematodes likely live in the biofilm, where they graze on mats of bacteria like tiny cows. Nematodes are incredibly tough organisms adapted to varying oxygen levels, food supply, and temperature, and can even reproduce without a mate. Nematodes also can persist in a hardy survival stage for thousands of years. Considering how tough nematodes are, Borgonie describes the warm mine water as “summer camp” for the worms.
If nematodes survive within rock fractures near the gold mines, they may live in similar areas throughout the crust, which would represent a huge source of biomass in the subsurface. Nematodes also may fulfill an important ecological niche by controlling bacterial populations and leaving behind wastes that fertilize the microbes.
Given the finding that seismic activity likely transports surface water and organisms into the subsurface, Borgonie proposes that future missions to Mars should drill for life at locations with evidence of earthquakes, or where deep water comes back to the surface. Previous studies have suggested that past conditions on Mars may have been more favorable to life than conditions today. It’s possible that seismic activity could have sequestered some life in the subsurface.
“If what we’ve found on Earth is any inkling of what we could find on Mars, we should go as soon as possible,” said Borgonie. “And if it’s a one-way trip, I’m going.”
Main image: Scientists have mainly looked for bacteria and archaea in the subsurface, but nematodes like these and other microscopic animals may represent an important part of the biomass in the crust. Credit: G. Borgonie, Extreme Life Isyensya