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Signs of life preserved in meteor glass

Complex organic material discovered inside meteor impact debris in Tasmania, is providing scientists with new clues about where to look, when searching for life on other planets.

The findings, reported in the journal Nature Geoscience, means asteroid and comet impact craters should be considered priority targets in any hunt for evidence of past life on other worlds.

"On planets like Mars, impact glasses may survive billions of years, possibly providing evidence for long extinct Martian organisms," says one of the study's authors Professor Phil Bland of Curtin University in Perth.

Bland and colleagues, including the study's lead author Dr Kieren Howard of the City University of New York, discovered the complex organic material encased in glassy ejecta, formed during a meteor impact in western Tasmania, 800,000 years ago.

The impact crated the 1.2-kilometre wide Darwin Crater, near Queenstown, Tasmania.

"When large meteors strike the Earth at incredibly high speeds of up to 18 kilometres per second, the energy released, causes solid rocks to melt and blast into the air," says Bland.

"The droplets of molten rock called tektites, then rain down over large areas, solidifying into glass fragments as they fall."

Tiny fragments of glass ejecta formed during the impact, which is known as Darwin Glass, have been found over a 400 square kilometre wide area radiating out from the crater.

"In this sort of glass, you don't really expect to see anything," says Bland.

"The default assumption is that it all got up to such high temperatures, that everything in it was destroyed or turned into charcoal."

Evidence of life

However, a closer examination of the glass melt from Darwin Crater, revealed tiny spheres of carbon rich material with complex organic signatures including cellulose, lignin, aliphatic biopolymers and protein remnants.

The glass had acted as a time capsule, with the oxygen-poor environment inside, preserving trapped organic material from degradation.

"This material told us that the asteroid which made the Darwin Crater, had crashed into an ancient rainforest and wet swampy environment," says Bland.

According to Bland, seperate evidence confirms that this was the local environment at the time of the impact.

Other worlds

"It's an exciting discovery, because it means you can get these little time capsules of trace evidence of what the environment was like when the asteroid hit, maybe millions of years ago," says Bland.

He says, there's every reason to believe that the same sort of impact glass found around Darwin Crater, would also be produced when meteors hit Mars.

"So it's possible that if there were environments on Mars where there was life, then we might see evidence of that in impact glasses sitting on the Martian surface," says Bland.

"Life in those environments might be long gone, but the trace evidence might still be there."