The soil has been around for 4.55 billion years,a decently long time. You might expect we’d have lots of rocks lying around that are very nearly that worn, but in fact they’re hard to find. The soil is active, or with erosion destroying worn material,stuff getting subducted down into the deep crust or mantle, and fresh land created by volcanoes burying older material. In fact, and finding truly ancient (say,more than four-billion-year-worn) rocks is tough.
Source: blastr.com