I have devised a way of colonising Mars by pantropy, (that is, by adapting life to the environment rather than terraforming it, which is exorbitantly expensive and time-consuming). The process involves excavating a network of tunnels beneath Mars. These tunnels and caverns are home to an underground ecosystem and subterranean lakes, kept warm by hydrothermal vents due to their depth. The problem is, due to a lack of sunlight, I need an alternative to photosynthesis for oxygen production.

So, I thought, what if self-replicating nanorobots were released which break down rock (silicon dioxide) into silica which they use to replicate themselves, and oxygen which they release as a by-product? These nanorobots form microbial mats covering the cave floor, and being inedible do not play a major role in the ecosystem except (obviously) in supporting it.

Eh? Eh?