But calling it an "intriguing" discovery and talking about water and "the base for life" based on that seems like a stretch to me...
If you dropped a molecule of methane into the atmosphere of Mars, it would survive about 300 years—that’s how long, on average, it would take for solar ultraviolet radiation and other Martian gases to destroy the molecule. By rights, the Martian atmosphere should have been scrubbed of its methane eons ago.
It could just leak out of subterrane entrapments, as they mention later in the article:
> They must have been of Martian origin—perhaps a burp from a relatively small and localized subsurface source to the north of the landing site. The Martian winds would blow that methane away over several months, explaining why the signal went away when it did.
However, we don't know the probability of all the steps leading to life actually taking place in the given time frame. The only reference value we have is earth, so it's just one data point and hardly possible to generalize. And mathematical estimations are difficult due to way too many factors to be considered (I've never seen one actually).
At the least we can say that formation of complex structures like DNA is far more complicated and thus less likely to form than methane, by orders of magnitude. So one could argue that it is generally far more likely for methane to be encountered than any (earth-like) life form.
Actually, there is: http://science.howstuffworks.com/environmental/earth/geology...