(Halicephalobus mephisto, aka "Mephisto"; Credit: Gaetan Borgonie, Ghent University, Belgium)
The world's deepest-dwelling multicellular organisms have just been identified, according to a paper in the latest issue of Nature. If you were to dig down about 2.2 miles, you might encounter Halicephalobus mephisto ("Mephisto") and its other nematode relatives.
You probably wouldn't want to go there, though.
Food at such a depth consists of bacteria. Temperatures are unbearably hot. There's no sex.
But for the nematodes, non-segmented worms measuring up to .02 inches long, the situation must be OK. They can take the heat, so to speak, and have evolved asexual reproduction.
"Carbon-14 data indicate that the fracture water in which the nematodes reside is 3,000- to 12,000-year-old palaeometeoric water," Borgonie and his colleagues write.
This type of water comes from underground sources and has low levels of oxygen, yet high amounts of sulphur and other dissolved chemicals. The overall region where this water exists is called the subsurface biosphere.
Scientists have known for some time that life exists at such depths, but they thought it mostly consisted of single-celled organisms. Prior experiments by another team found algae, fungi and amoebae about 656 feet beneath the U.S. surface. Fungi was also discovered approximately 1,476 feet below terra firma in Sweden.
Nematodes were known from these higher levels, but Halicephalobus mephisto is a new species.
Here's how Borgonie and his team describe its name: "Mephisto (from Mephistopheles, pseudo-Greek): ‘‘he who loves not the light,’’ alluding to the Devil, Lord of the Underworld, in reference to the Faust legend in medieval mythology because the new species is found at a depth of 1.3 km (4,265 feet) in the Earth’s crust."
That measurement is a minimum, however, as the researchers believe nematodes also exist 2.2 miles down.
As deep as this worm lives, it may be connected to possible life in outer space. That's because extreme conditions on Earth may be somewhat similar to environments on other planets.
As the scientists conclude: "Our results expand the known metazoan bio-sphere and demonstrate that deep ecosystems are more complex than previously accepted. The discovery of multicellular life in the deep subsurface of the Earth also has important implications for the search for subsurface life on other planets in our solar system."
According to a report in Discover Magazine, Borgonie and his team may next look for nematodes in the sediments beneath ocean floors.