[yungchin]

The context for that quote was missing I think (that is, missing from the original article, not your comment), but it makes more sense if they're talking about turning rock into fertile soil.

You would have had a whole succession of different types of plants to slowly work the rock surface. Then humans show up, rip out all the trees that kept that hard-won top soil in place, and it all runs off out to sea in no time. Basically it's about places like Iceland, not Iowa, I guess.