A Martian landscape on Earth

Lakes: Acidic bodies of water in a remote part of Australia offer clues to what forms of life could once have thrived on the red planet - if any.

Medicine & Science

March 29, 2004|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

To reach Australia's Kalgoorlie lakes, you fly west from Sydney, across the outback to Perth. From there, you can drive inland for 12 hours, or catch a plane. But after landing in the dusty gold-mining town, you'll have to rent a Jeep before the shops close at 5 p.m., and then strike off into the desert on your own.

Kathleen C. Benison and her geology team made the long trip from Central Michigan University in 2001 to study the cluster of highly acidic salt lakes, which she says bear a striking resemblance to waters that once flowed on Mars.

Data from NASA's Mars rover Opportunity have convinced scientists that the planet's Meridiani Planum once flowed with salty, acidic water sufficient to sustain life.

While there's no evidence yet that Martian life did evolve to swim at Meridiani Planum, Benison said there's life in Kalgoorlie's equally inhospitable waters: So why not Mars?

"In recent decades we have found all these microbes on Earth that we didn't know could exist," she said. "Maybe there are different types of life on Mars than we understand. The key is being open-minded, trying to think of all the possibilities and ... how to test for them."

Mars rovers

Since its landing on Jan. 25, Opportunity has been looking for evidence that Mars once had enough liquid water to sustain life.

Last month, scientists announced they had identified a rocky outcrop bearing the mineral jarosite. It's rare on Earth because it forms under unusual circumstances - in lakes, hot springs or ground water that contain sulfuric acid.

Close-up pictures of Mars rocks revealed curious pockmarks and tiny, BB-size spheres which scientists dubbed "blueberries."

Geologists recognized the pocks as "vugs," or cavities left in rocks after the erosion of fragile salt crystals. The crystals first formed in the porous rock as the ground water evaporated. The spheres, they said, are hematite "concretions," formed as salty ground water evaporates and dissolved minerals come out of solution.

Last week, geologists said Opportunity had found sedimentary rocks that contained evidence of rippling in Martian sediments. Such rippling is caused by flowing water.

After 58 days on Mars, Opportunity had answered the central question the $840 million mission was designed to resolve: "This was a shallow sea very suitable for life," said Steven Squyres, science team leader for the Mars rovers.

It was all familiar geology to Benison. She has studied the same kinds of minerals for years, beginning with her doctoral research into the origins of red sandstones and shales in Kansas and North Dakota. The rocks formed in the Permian era, about 270 million years ago, across 77,000 square miles of what are now the Northern Great Plains.

"I was trying to figure out what kinds of environments they existed in," she said. Using laser microprobe spectroscopy, she analyzed tiny droplets of water trapped within salt crystals embedded in the rocks. The water was highly acidic.

`Like battery acid'

Acidity is measured on a pH scale. Most natural waters have a pH around 6, 7 or 8. Higher numbers are more alkaline. Lower numbers indicate more acidic conditions.

The pH of the Permian water droplets ranged from 1 to less than zero. "These were super-acidic, like battery acid," she said.

Nature makes acids easily. Sulfur bonded to a metal like iron makes a sulfide, such as pyrite or "fool's gold." Expose that to water and oxygen and you get sulfuric acid.

The hard part is maintaining it. "Usually in nature there's something in the sediment that can buffer the acid," Benison said. The mineral feldspar or common carbonates will instantly neutralize acids.

But where rocks and soils have been exposed on the surface for millions of years, all the potential buffers can be weathered away. Then, she said, "if you make acid, there's nothing there to buffer it, and maybe it can survive."

That appears to be what happened in Permian Kansas and North Dakota, and more recently in Western Australia, Benison said.

The briny lakes near Kalgoorlie had pH readings of 2 and 3. "Nobody goes near the lakes," Benison said. Even the kangaroos and emus steer clear.

The lakes are small - the biggest just a mile wide. Everywhere, the blue water is shallow enough to walk across, surrounded by dry flats of red mud rimmed with a white salt crust where the water has evaporated.

Life under the surface

Kalgoorlie has ignored its salty lakes. The town pipes its drinking water from desalinization plants in Perth. Few people even realized the waters were acidic. Benison was the first to describe their geology.

But as inhospitable as the Kalgoorlie lakes seem, they do shelter microscopic life. "We do have a culture of bacteria we were able to get from those samples," said University of Missouri biologist Melanie Mormile, who is working with Benison. They're growing in a medium with an acidic pH of 4. "We're trying to figure out now what they are.

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