Methane is a tantalizing sign of life. It is easily broke up in the presence of the gases, the carbon part turning into carbon dioxide, the hydrogen part into water. As it breaks down so easily, it needs a good source on the surface of any planet in order to then be present in the atmosphere. On earth, our Methane mostly comes from our vast numbers of cows. And in general, it is considered a good sign of some sort of life.
New results from Curiosity rover has now detected wafts of methane in the Martian air. The waft is the key here. Although Methane on Mars has been detected before, in 2009, it is the relative quick bursts that is so tantalizing this time around. There was nothing, then it was present at pretty high levels, and then gone within hours. This quite sudden release is possibly a sign of some sort of biological activity. No one is claiming anything definite yet regarding life on another planet, but this could be one of the best signs yet that we are not alone.