The idea is that each SRP unit makes 2 copies of itself and then moves off to perform another task, such as finding raw materials.
By this "power of 2" you get exponential growth.
At the mechanical level, 3D printing and robots allow self-construction.
At the biological level, plants like sunflowers can take up things like zinc, copper, and radioactive elements. (https://pubmed.ncbi.nlm.nih.gov/22567714/) If we can figure out how this is done perhaps we can find a genetic basis. If so, we could engineer ants that would naturally mine materials.
If nothing else, at least we can cover Mars in paperclips :-) (https://en.wikipedia.org/wiki/Instrumental_convergence)
In any case, I'm happy to see that NASA is interesting in terraforming Mars. Maybe my research will find it to be a practical application.