Now this does increase the chances of finding life on Mars but it also increases the chances that that life would have originated on Earth not Mars. A further reason that any life found on Mars would have most likely originated on Earth is that the areas of Mars known to have had surface water in the past where actually lakes of sulfuric acid not habitable seas. These are three main ways Earth Bacteria could have reached Mars. They could have hitched a ride on Earth rocks ejected into space by impacts; they could have gotten there by riding dust particles and the most likely possibility it that they were carries there by are own probes. Questions have been raised as to how successfully various probes have been sterilized making contamination possible.
Given the Catastrophic nature of Martian Geology Mars would be a interesting place with or without life but before any declaration of life on Mars or any other planetary body in to solar system scientists better get a genetic sample because that life would have a good chance being from Earth.