A very good summary here
https://boards.straightdope.com/t/yet-an.../1022940/7
Quote:In this case, the Perseverance rover found vivianite (which is often found attached to fossilized bone or within the shells of bivavles) and greigite (which is formed by magnetotactic bacteria that occupy hydrothermal vents on Earth). To my understanding (I am definitely not an expert it geochemistry), the known pathways for forming these minerals at terrestrial temperatures requires the decay of organic matter or transformation by bacteria in iron-bearing substrate, and the only pathways of developing these minerals without the presence of living system require very high temperatures for which this is no evidence were present on the surface of Mars which this material was deposited. That leaves open the possibility of formation elsewhere near a volcanic or hydrothermal vent during the period that Mars was still tectonically active and was then deposited later at this location through hydrologic activity
Quote: in essence they suggest that the iron–phosphate bearing minerals are unlikely to have formed absent of the presence of carbon-rich organic matter in “post-depositional redox reactions“ (in other words, reduction-oxidation actions catalyzed in place by the activity of some energy-mediating system). The section of the paper labeled “An exploration of reaction mechanisms“ posits a null hypothesis—that is, a thesis that would provide an abiotic (non-living) path to producing these minerals—and then disprove it by arguing that there was no evidence of sufficient conditions for this process to have occurred
I'm not sure the 'null hypothesis' has been disproved, yet, but this looks very promising. If life was on Mars in the past, it probably isn't there now, unless it is deep underground, like the Deep Hot biosphere on Earth. There is also no guarantee that the life on Mars (if it ever existed) originated there - it is possible that any life found on Mars, living or dead, originally came from Earth and was transferred there by 'lithopanspermia' ( the transfer of life-bearing rocks following energetic meteoric impacts) or by some other (possibly gentler) method.