It's also just wrong. Maybe this is true under "natural conditions" (however you want to define those). But intentional farming practices can produce this much

It's also just wrong. Maybe this is true under "natural conditions" (however you want to define those). But intentional farming practices can produce this much top soil every year. The problem is that few farmers use those practices. But I do, and I can tell you that planting green fertilizers and nitrogen-fixing cover crops, and then plowing them under, will produce pretty good topsoil very quickly.