Volcanic rocks found to be teeming with bacteria offer hope for life on Mars

Tiny cracks inside volcanic rocks that harbour billions of bacterial microorganisms could give clues about how to find life on Mars, Japanese researchers have suggested.

Scientists at the University of Tokyo finally developed a new method to examine the interior of these cracks after more than a decade of trying.

They estimated that the cracks hold about 10 billion bacterial cells per cubic centimetre, orders of magnitude more than the average density of bacteria living in mud sediment on the seafloor, which is around 100 cells per cubic centimetre.

“I am now almost over-expecting that I can find life on Mars. If not, it must be that life relies on some other process that Mars does not have, like plate tectonics,” said associate professor Yohey Suzuki from the University of Tokyo.

“I thought it was a dream, seeing such rich microbial life in rocks,” said Suzuki, recalling the first time he saw bacteria inside the undersea rock samples.

Undersea volcanoes spew out lava at approximately 1,200°C, which eventually cracks as it cools down and becomes rock.

The cracks are narrow, often less than 1mm across. Over millions of years, those cracks fill up with clay minerals which bacteria can then use to multiply.

“These cracks are a very friendly place for life. Clay minerals are like a magic material on Earth; if you can find clay minerals, you can almost always find microbes living in them,” Suzuki said.

The microbes identified in the cracks are aerobic bacteria, meaning they use a process similar to how human cells make energy, relying on oxygen and organic nutrients.

The rock samples used in the experiment were originally collected in late 2010, kilometres below sea level underneath the ocean floor.

The rock samples were estimated to be up to 104 million years old and the collection sites were not near any hydrothermal vents or sub-seafloor water channels, so the researchers believe the bacteria arrived in the cracks independently rather than being forced in by a current.

Suzuki spent years trying to find a way to analyse the bacterial content of the rocks without destroying them. Ultimately he coated them in a special epoxy to support their natural shape so that they wouldn’t crumble when he sliced off thin layers.

These thin sheets of solid rock were then washed with dye that stains DNA and placed under a microscope.

Whole-genome DNA analysis identified the different species of bacteria that lived in the cracks. Samples from different locations had similar, but not identical, species.

Suzuki and his colleagues speculate that the clay mineral-filled cracks concentrate the nutrients that the bacteria use as fuel. This might explain why the density of bacteria in the rock cracks is eight orders of magnitude greater than the density of bacteria living freely in mud sediment where seawater dilutes the nutrients.

He speculates that the clay minerals filling cracks in deep ocean rocks are likely similar to the minerals that may be in rocks on the surface of Mars.

“Minerals are like a fingerprint for what conditions were present when the clay formed. Neutral to slightly alkaline levels, low temperature, moderate salinity, iron-rich environment, basalt rock – all of these conditions are shared between the deep ocean and the surface of Mars,” he said.

The researchers are now collaborating with Nasa to design a plan to examine rocks collected from the Martian surface by rovers.

Ideas include keeping the samples locked in a titanium tube and using a CT (computed tomography) scanner, a type of 3D X-ray, to look for life inside clay mineral-filled cracks.

“This discovery of life where no one expected it in solid rock below the seafloor may be changing the game for the search for life in space,” Suzuki said.

Last year a team from Edinburgh University demonstrated that microscopic tubes and filaments found within rocks that resemble the remains of tiny creatures may actually have been formed by chemical reactions. It is hoped this could make it easier to avoid false positives when determining whether Mars rock harboured life.

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