This appeared at New Scientist back in 2006, but it seems pretty important to thinking about what Curiosity is up to now:
[A] paper by Rafael Navarro-Gonzalez of the University of Mexico and others demonstrates that the GCMS instrument [organic detection device used in the 1976 Viking missions] was incapable of detecting organic compounds even in Mars-like soils from various locations on Earth. This includes parts of Chile’s Atacama desert where other tests prove that living microbes are indeed present.
In some soils – including samples taken from Rio Tinto in Spain, which contain iron compounds similar to those detected in Mars soils by NASA’s rover Opportunity, the sensitivity of the GCMS was actually a million times lower than its claimed threshold for detection, says Navarro-Gonzalez.
In other words, organic molecules may yet be in Martian soil, and Curiosity, with its more sophisticated GCMS, may find them. And the implication is this: if they’re found it means that extremophiles (microorganisms that thrive in extreme environments) may be lurking on Mars’s desert surface and may have been responsible for the positive results acquired from the 1976 Viking missions’ life experiment known as “labelled release” (LR).
Follow the organic molecules, Columbo.
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Here’s an image of a mat of orange extremophiles surrounding blue and sterile hot water in Yellowstone (image source: Wikipedia Commons):
Prometheus Unbound 
