Just what would produce the methane isn’t clear. It could represent recent or even current microbial life (possibly underground), but it could also geothermal reactions or ages-old methane finally escaping to the surface. The one certainty is that any gas will have appeared relatively recently — reactions with sunlight and chemicals would split the molecules within centuries.
If scientists can confirm the presence of methane, the greater challenge is finding ways to study it in more detail. The Mars 2020 rover and other upcoming vehicles are meant to look for the ingredients of life, but not to verify the possibility of existing life. It could be a long time before there’s a definitive pronouncement on what the gas represents.