Scanning electron micrographs of some of the Eukarya recovered from water up to 1.4 km underground at mine sites in South Africa.

Scanning electron micrographs of some of the Eukarya recovered from water up to 1.4 km underground at mine sites in South Africa.Credit: G. Borgonie (ELi); Used under CC by 4.0.

Uncovering the Mysteries of a Subterranean Zoo

Exciting deep water discoveries of complex life may suggest there is more on Mars.


Where there is water, there is potential for life. Even under the most extreme conditions, researchers are finding life where it isn’t expected: under scorching temperatures, crushing pressures, and poor access to light and nutrients.

A few examples include the tube worms that are at home at the hydrothermal vents of the deep sea, and the tardigrades found all over the world that can even withstand the radiation and vacuum of outer space.

Even our knowledge of the locations of water are expanding. The world’s oldest liquid water was found in 2013, dated at over 1.5 billion years old, at a mine in Timmins, ON. Evidence of ancient ocean water cycling into the deep Earth has been found trapped in so-called ugly diamonds. Earlier this year, NASA made a landmark announcement that liquid water had been found flowing on the surface of modern day Mars.

A veritable subterranean zoo expands the definition of the Earth’s habitable biosphere

Until recently, life was not expected deep underground. Even when single-celled microbial life was found in rock fractures 3 kilometres underground, the discovery of a multi-celled worm at similar depths was dismissed as a fluke.

Work published in Nature Communications has authors calling specimens collected 1.4 km deep a “veritable zoo” of multi-celled organisms. The study was led by Gaetan Borgonie of the non-profit group Extreme Life Isyensya and co-authored by Canadian researcher Barbara Sherwood Lollar at the University of Toronto.

The team descended into tunnels drilled over 3 km into the ground at South African mine sites, collecting water pouring out of bore holes and filtering it for specimens. They uncovered 17 different species of microscopic invertebrate animals, including: a variety of worms, aquatic creatures called rotifers, and a potential new species of crustacean called a copepod.

Although most of the specimens found have cousins known to live closer to the Earth’s surface, researchers also ruled out contamination of the water samples with material from above ground. This discovery expands the definition of the Earth’s habitable biosphere.

Conditions underground are stable and well-suited to life

Sherwood Lollar notes that the water found in these deep systems is rich in materials that would make good food sources for micro-organisms. The water contained the right balance of salt that indicates extensive water-rock reaction that can free energy-rich chemical compounds for underground animals to eat.

Although a subterranean life may sound inhospitable, the conditions there are relatively stable when compared to life above ground, where conditions can change by the hour, and many factors could cause extinction. This evidence of complex life deep underground bolsters hope for finding life on Mars, where subterranean life may be shielded from the radiation that bombards the surface of the planet.

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Karyn Ho is a science animator and engineer who thrives at the interface between science, engineering, medicine, and art. She earned her MScBMC (biomedical communications) and PhD (chemical engineering and biomedical engineering) at the University of Toronto. Karyn is passionate about using cutting edge discoveries to create dynamic stories as a way of supporting innovation, collaboration, education, and informed decision making. By translating knowledge into narratives, her vision is to captivate people, spark their curiosity, and motivate them to share what they learned.