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LIFE might eke out an existence far deeper inside Earth than we imagined. Samples from a mud volcano contain biological signatures that suggest microbes lived in the material when it was several kilometres beneath the ocean floor.

“We might have a very big biosphere below our feet that’s very hard to get to,” says .

Other researchers agree life could exist at such depths, but say the case is not yet proven. “They don’t have conclusive evidence,” says Rocco Mancinelli, an astrobiologist at NASA’s Ames Research Center, who studies life in extreme environments.

“We might have a very big��biosphere deep below our feet that’s very hard to��get to”

Plümper’s team studied 46 samples drilled from the South Chamorro mud volcano, near the deepest part of the ocean, the Mariana trench. Here, one tectonic plate slides under another. The heat and stress causes some of the material on the subducting plate to become a buoyant mineral called serpentinite that rises and erupts out of mud volcanoes.

Examining the serpentinite in their samples, the team found chemicals usually produced by life, including amino acids and hydrocarbons.

Given that some microbes can withstand temperatures as high as 122°C and pressures about 3000 times higher than at Earth’s surface, Plümper calculates that life could survive up to 10 kilometres beneath the seabed.

There have been several recent reports of life at great depths, with��nematode worms found living 3��kilometres down in a gold mine, for��instance. But if Plümper is right, life can survive far deeper still.

Mineral reactions at these depths would provide the carbon, nitrogen and energy life needs, says Mancinelli. But the chemicals found by Plümper’s team might have been produced by processes that don’t involve life, he adds.

This article will appear in print under the headline “Life could exist up to 10 km below sea floor”

Read more:��Deep life: Strange creatures living far below our feet,��Life is found in deepest layer of Earth’s crust