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Organic carbon on Mars didn't come from living things, study says

May 24, 2012|By Eryn Brown, Los Angeles Times / For the Science Now blog
  • An electron-microscope photo of the famous Martian meteorite ALH 84001. A new analysis has shown that organic carbon in such Mars rocks did not come from biological sources.
An electron-microscope photo of the famous Martian meteorite ALH 84001.… (NASA )

Life on Earth is based on organic molecules — so when scientists have found these carbon-based compounds in meteorites from Mars, many can’t help but get excited. Might the presence of organic carbon in Martian rocks be a sign of ancient life on the Red Planet? Were the molecules carried to Mars from Earth or someone else in the solar system?  Or did they arise on the planet, a product of Martian geology?

The questions have been a subject of debate for decades, flaring up periodically when an object of interest comes along, offering tantalizing clues of life beyond. One of the most famous cases of Martian meteorite mania occurred in 1996, when a NASA scientist announced that a meteorite known as ALH 84001 contained microscopic tracks that appeared to be fossils of tiny bacteria.  The claim captured the attention of then-President Bill Clinton (who spoke about the discovery in the Rose Garden) and helping to secure funding for the young field of astrobiology.

But a study published online Thursday in the journal Science (subscription required) adds weight to arguments that the carbon in Martian meteorites does not come from biological sources, after all.

Andrew Steele of the Carnegie Institution in Washington, D.C., and colleagues analyzed samples from 11 Martian meteorites including ALH 84001. They detected carbon compounds, enclosed in grains of crystallized minerals, in 10 of them. The placement of the molecules inside the crystals showed that the carbon compounds were formed by volcanism on Mars, and not by biological processes, they wrote.

This could seem like a blow to the life-on-Mars camp, but, as the magazine New Scientist pointed out here, the team’s analysis might also bolster arguments favoring the existence of extraterrestrial life — by showing that the same organic molecules believed to have helped build life on Earth also exist on other planets.

"The presence of organic carbon at or near the Martian surface provides a potential nutrient source for putative life," study co-author Francis McCubbin told New Scientist.


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