Source: BBC

Just how far down in the Earth’s crust can animals survive? In the dark, hot depths of several South African gold mines, there live some tiny worms that may hold the key to answering that question.

These creatures are the deepest living animals that have ever been discovered.

No one knows how they got down there, but they could have been living in the mines for thousands of years. Their very existence suggests that complex life can survive far deeper in the Earth than was ever thought possible.

Halicephalobus mephisto was named for a demon (Credit: Gaetan Borgonie et al)

In the 1980s, scientists discovered that life can endure thousands of feet beneath the Earth’s surface.

Nematodes can transform into a special form called the dauer stage

However, most scientists believed that the bowels of the Earth could only house single-celled organisms like bacteria. In the deep Earth it is hot and dark, and there is very little oxygen. There is also not much food down there, so any animal making its home in the belly of the Earth would struggle to get a decent meal.

One scientist thought differently. Gaetan Borgonie was previously at the University of Ghent in Belgium and is now at Extreme Life Isyensya in Gentbrugge, Belgium. He was convinced that one animal could survive deep down in the Earth’s crust: a nematode worm.

That is because nematodes are extremely hardy, able to cope with extreme heat, cold and dehydration. They have an ingenious trick that allows them to survive.

A nematode on biofilm (Credit: Gaetan Borgonie/Nature Communications)

Nematodes can transform into a special form called the dauerstage. In this form, they can survive harsh conditions for long periods before reawakening when the going gets good again.

Surely if any animal could live deep inside the Earth it would be this hardy worm?

This makes them similar to tardigrades: tiny creatures that can survive being boiled, frozen, crushed, dried out or blasted into space by going into a kind of stasis.

In the dauer stage, the nematode goes into stasis and its metabolism slows. The stage is triggered by a pheromone and occurs when there is a lack of food, high temperature, or overcrowding.

Nematodes in the dauer state are spectacularly resilient. When the space shuttle Columbia broke up after re-entering Earth’s atmosphere in 2003, there were nematodes on board:they survived both the disintegration and the fall back to Earth.

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