I just finished listening to 'Collapse' by Jared Diamond and it goes over Iceland a bit. They've got serious ecological problems because of soil. Most of their soil comes from light volcanic ash, which replenishes at a much lower rate than other places with tons of vegetation and rivers and other things contributing.
Soil, generally, is surprisingly delicate stuff. It accumulates at the rate of about an inch per century under natural conditions on such abundant landscapes as the US plains. That's slow, but over the 10,000 year span since the last ice age, it's enough for 100 inches or so to accumulate (about 250 cm).
Much of that isn't deposited but fixed from the air by plants which then decay in place, though the freshly-arrived material often provides vital micronutrients -- itself a problem in Australia where the lack of geological activity means that there is very little of these materials, limiting ag productivity.
In regions with harsh climates and short growing seasons (e.g., Iceland), there's little time for soil-forming processes to set hold, and the slight progress made can be undone quickly. Even in places that appear full of life, conditions may remove soil or nutrients, e.g., tropical rainforest.
If I think of things that may bring doom to humans, I tend to think a lot about dirt and bugs and plankton and algae.
