Dissociation of water might seem a good source, but not enough oxygen is observed. Spectrometers a. Atmosphere is secondary, from volcanic degassing. No plate tectonics found or indicated. Content is mostly lava, basalt rocks and soil, with Permafrost a few meters down, at most. Chemical reactions are NOT due to life.
Martian soil has lots of peroxides, especially with iron.
There are a great many books and articles about Mars, and the spacecrafts Mariner, Viking, and Rover in particular. We list a few, in case you are really keen and want to find out more about some aspect of the topics just touched on here. Be aware in your reading that some of the material rushed to press shortly after the Viking and Pathfinder landings has not stood the tests of time and now would be classified more as science fiction or wishful thinking than scientific fact. The space programme, with its need for public relations, suffers a lot from undigested prognostications, especially when prodded by the media's falsely perceived need for immediate results.