I Potential biosignature found in Mars rock

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TL;DR Summary

A NASA rover found chemicals that are difficult to explain without life.

Publication: Redox-driven mineral and organic associations in Jezero Crater, Mars
Article: NASA Says Mars Rover Discovered Potential Biosignature Last Year
Press conference

The combination of these minerals [vivianite (hydrated iron phosphate) and greigite (iron sulfide)], which appear to have formed by electron-transfer reactions between the sediment and organic matter, is a potential fingerprint for microbial life, which would use these reactions to produce energy for growth. The minerals also can be generated abiotically, or without the presence of life. Hence, there are ways to produce them without biological reactions, including sustained high temperatures, acidic conditions, and binding by organic compounds. However, the rocks at Bright Angel do not show evidence that they experienced high temperatures or acidic conditions, and it is unknown whether the organic compounds present would’ve been capable of catalyzing the reaction at low temperatures.

The ~100 authors don't find a good way this could have formed without life, but also can't rule it out. Now that they have shared their findings with the larger community someone else might find an explanation - or maybe it was actually made by life.

 

[BillTre]

Here is some related information:

One of the main origin of life on earth scenarios involves the interaction of fluids from serpentinization of basalt raising up through undersea sediments and interacting with chemically different seawater across an interface partly composed of greigite. This is supposed to allow redox reactions between the low pH seawater and the high pH serpentization fluids. The pH difference is favors the two sides of the reaction at the different pH's.

This is a prebiotic reaction to build organic compounds before life was around.