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"It's like finding Moby **** in Lake Ontario," says Tullis Onstott of the
nematode worms his Princeton University team discovered living far
beneath the Earth's surface in South Africa.
The tiny worms – just 500 micrometres long – were found at depths
ranging from 900 metres to 3.6 kilometres, in three gold mines in the
Witwatersrand basin near Johannesburg. That's an astonishing find given
that multicellular organisms are typically only found near the surface of the
Earth's crust – Onstott's best guess is in the top 10 metres.
The creatures seem to live in water squeezed between the mines' rocks,
can tolerate temperatures reaching 43 °C and feed off bacteria. Carbon
dating of compounds dissolved in the water suggests that the worms have
been living at these depths for between 3000 and 12,000 years.
"To have complex life sustain itself for such a long period completely sealed
away from everything else – from sunlight, from surface chemistry – is
pretty amazing," says Caleb Scharf of the Columbia Astrobiology Center in
New York City.
No place for a worm
Onstott says no one thought multicellular organisms would be found living
in this so-called fracture water. He points out that microbiologists are still
trying to prove and understand how even single-celled organisms can exist
at these depths. "The lack of oxygen, temperature and food is a big
dissuader," he says.
"We've had this preconception that there can only be certain types of
organisms in certain environments," says Scharf. "But it's not true at all.
There are more complex organisms in these bizarre environments."
Animals on Mars
If complex life forms are able to survive inside cracks deep inside Earth, it
raises the possibility that they might have survived undetected in similar
environments on Mars.
Carl Pilcher, director of NASA's Astrobiology Institute in Moffett Field,
California, points out that Onstott has previously discovered a bacterium
living 2.8 kilometres underground, completely isolated from all other
ecosystems on Earth (Science, DOI: 10.1126/science.1127376). The bug
gets its energy from the radioactive decay of elements in the surrounding
rocks. "The significance was that you could imagine an ecosystem existing
in the subsurface of a planet that didn't have a photosynthetic biosphere,
like Mars," he says.
Until now, it was thought such an ecosystem could be made of bacteria
only. But Onstott's new findings have completely changed that. "It has
extended the [earlier] work to an animal," says Pilcher.
"These nematodes are grazing on microbes. So now you could imagine that
if animal life had ever developed on a planet, and the surface of that
planet became lifeless," Pilcher explains, "you could imagine that animals
[small enough to fit in tiny cracks] could coexist with microbial ecosystems
all powered by radioactivity."
The worm is called Halicephalobus Mephisto
nematode worms his Princeton University team discovered living far
beneath the Earth's surface in South Africa.
The tiny worms – just 500 micrometres long – were found at depths
ranging from 900 metres to 3.6 kilometres, in three gold mines in the
Witwatersrand basin near Johannesburg. That's an astonishing find given
that multicellular organisms are typically only found near the surface of the
Earth's crust – Onstott's best guess is in the top 10 metres.
The creatures seem to live in water squeezed between the mines' rocks,
can tolerate temperatures reaching 43 °C and feed off bacteria. Carbon
dating of compounds dissolved in the water suggests that the worms have
been living at these depths for between 3000 and 12,000 years.
"To have complex life sustain itself for such a long period completely sealed
away from everything else – from sunlight, from surface chemistry – is
pretty amazing," says Caleb Scharf of the Columbia Astrobiology Center in
New York City.
No place for a worm
Onstott says no one thought multicellular organisms would be found living
in this so-called fracture water. He points out that microbiologists are still
trying to prove and understand how even single-celled organisms can exist
at these depths. "The lack of oxygen, temperature and food is a big
dissuader," he says.
"We've had this preconception that there can only be certain types of
organisms in certain environments," says Scharf. "But it's not true at all.
There are more complex organisms in these bizarre environments."
Animals on Mars
If complex life forms are able to survive inside cracks deep inside Earth, it
raises the possibility that they might have survived undetected in similar
environments on Mars.
Carl Pilcher, director of NASA's Astrobiology Institute in Moffett Field,
California, points out that Onstott has previously discovered a bacterium
living 2.8 kilometres underground, completely isolated from all other
ecosystems on Earth (Science, DOI: 10.1126/science.1127376). The bug
gets its energy from the radioactive decay of elements in the surrounding
rocks. "The significance was that you could imagine an ecosystem existing
in the subsurface of a planet that didn't have a photosynthetic biosphere,
like Mars," he says.
Until now, it was thought such an ecosystem could be made of bacteria
only. But Onstott's new findings have completely changed that. "It has
extended the [earlier] work to an animal," says Pilcher.
"These nematodes are grazing on microbes. So now you could imagine that
if animal life had ever developed on a planet, and the surface of that
planet became lifeless," Pilcher explains, "you could imagine that animals
[small enough to fit in tiny cracks] could coexist with microbial ecosystems
all powered by radioactivity."
The worm is called Halicephalobus Mephisto
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