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  Precious opals in Australia may shed light on the origin of the surface of Mars


June 22, 2013


Research on how precious opals were formed in Australia could provide astrobiologists with insight as to what may have happened on the surface the planet Mars, according to Patrice Rey, a scientist at the University of Sydney.

Precious opal is predominantly found in the red earth of the Great Artesian Basin in central Australia, within 50 meters of the surface. Like common opal, they are comprised of amorphous spheres of silica 150 to 400 nanometers wide, but in precious opal they are arranged in orderly arrays, thereby producing scintillating colors.

According to Rey, it has long been a mystery why precious opal was found so abundantly in the Great Artesian Basin, and almost nowhere else on Earth. In his opinion, it is because the Great Artesian Basin was once filled by the Eromanga Sea, which at its peak covered about 60 percent of the Australian continent.

Opal, Rey discovered, was the result of acidic oxidative weathering during the drying out of the Eromanga Sea, starting about 100 million years ago. Such acidic oxidative weathering is unusual on Earth, largely because the planet's surface usually includes carbonates that neutralize acid.

Now is where it gets particularly interesting, especially if you are an astrobiologist.

According to Rey, acidic oxidative weathering has also been seen on the surface of Mars, which evidently shares a number of other features with the Great Artesian Basin, including types of rocks, a similar history of flooding then drying out, mineralogy and color."

"It costs billions of dollars to send rovers and orbiters to Mars," Rey told the media. "Therefore, looking right here on Earth for ancient and modern analogs to Mars' environment is key to carrying on research in greater detail and explore the role biology has in weathering processes."

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