News in Science

Mars' minerals could be microbe made

Biological origins New Australian research suggests Martian minerals may have formed from biological rather than geological origins.

The findings, reported in the journal Geology, indicate the mineral stevensite, which is found on both Earth and Mars, can be created either in hot, highly alkaline volcanic lakes, or by mineralisation in living microbes.

Stevensite is a magnesium-silicate mineral, used a Nubian beauty treatment for several centuries.

"There's an old lake in Morocco where stevensite deposits were mined and distributed by camel caravans as far east as India," says the study's lead author Dr Robert Burne of the Australian National University (ANU). "It's quite possible that Cleopatra used stevensite as a treatment for her skin and hair."

According to Burne, stevensite was detected by NASA's rover missions, which have been associated with spherulites [small spheres of unknown origin]," says Burne.

"But our finding - that stevensite can form around biological organisms - will encourage re-interpretation of these Martian deposits and their possible links to life on that planet," he says.

'Garden of Eden'

Burne and colleagues at the ANU and University of Western Australia, recently examined a series of reef structures in the waters of Lake Clifton south of Perth.

"Instead of a boiling volcanic soda lake, Lake Clifton was like a 'Garden of Eden', an idyllic location with crystal clear waters and neutral pH," says Burne.

The researchers found the masses in the lake were formed as mineral deposits.

"These deposits accumulated over the past 2000 years into rigid reef structures which we've named microbialites, and which are similar to some of the oldest structures formed by life on Earth," says Burne. "Microbialites are the earliest large-scale evidence of life on Earth."

"They demonstrate how microscopic organisms are able to join together to build enormous structures that sometimes rivalled the size of today's coral reefs."

Fossilised microbes

Scientists originally thought the microbialites were made of calcium carbonate.

"But after closer examination we discovered the calcium carbonate was only coming in afterwards, and the initial structural rigidity of these things was made up by the mineral stevensite, which was totally unexpected."

The stevensite forms through the microbe's outer sheaths, which are rich in organic chemicals, creating an environment where minerals precipitate out of the surrounding water and over generations form the microbialite structures.

"Later on as part of the ongoing process the stevensite is replaced by calcium carbonate, which completely obliterates the evidence of the microbes," says Burne.

"So you end up with a mass of limestone that was initially formed by microbes, but there's no trace of those microbes left."

The findings also have implications for how some of the world's largest oil reservoirs were formed.

Epilogue

Unfortunately development in Lake Clifton area over the past three decades has meant its once pristine environment is no more.

"The tragedy of Lake Clifton is that when we first studied it in 1984, it was in a pristine state and the microbial mats were still in place," says Burne.

Recent development and subdivisions in the area has resulted in the introduction of invasive species such as black bream and nutrient run off into the lake promoting algal growth which has swamped the microbialite.

"So you've got a combination of developmental mistakes that have essentially destroyed what was a truly unique ecosystem which reflected what had been going on during the Cambrian epoch 600 million years ago," says Burne.