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What Life Leaves Behind: Chemical Fingerprints of Organisms on Other Worlds?
from Seed
In 1976, NASA's twin Viking landers arrived on Mars, equipped with four experiments designed to offer foolproof evidence of life on the Red Planet. They were looking for biosignatures, or fingerprints of life. As they took their first scoops of Martian soil, the whole world held its breath.
The first experiment incinerated a sample of soil and analyzed the resulting hot gas for organic carbon, but none was detected. The second and fourth sprinkled nutrients and then carbon on two more soil samples, hoping to incite a feeding frenzy in any dormant Martian microbes, but the results were the same as with controls.
But it was the third--the labeled release experiment--that found something in the sere red dirt would absorb a tracer of radioactive carbon and send it up in a steady plume of carbon dioxide, just as a living, respiring cell would. There was life on Mars, or so it would seem.
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