I was just browsing through some astronomy magazine and there was a bit on methane and possibly life on mars. Apparently if there was life on mars, to produce the observed gas emmisions it would consist of a total biomass of 20 tons.
As much as i would like to think there is life on mars, this estimate puts that in great doubt.
You could get 20 tons easy even in the driest square mile of the sahara desert, and that's supposed to represent the maximum amount of biology for an entire planet?
Mars isnt a very hospitable place, but i would think that life generaly evolved to fill every niche it can, and unless there is a rational explanation for all that missing methane gas, maybe it's just geological emissions.