At the beginning of its history, Mars was much more welcoming, with vast expanses of liquid water and active volcanism, like the young Earth. Life could very well have appeared and take the time to adapt to conditions slowly becoming increasingly difficult. Just as terrestrial methanogens exist in the soil, and even at great depth in the rocks, some descendants of the first similar Martian microorganisms could still exist, and this may be in the vicinity of the Martian volcanoes. It would therefore be their methane generating activity that would be detected today by the Martian probes.