The thin layer of topsoil that covers much of the earth's land surface is the foundation of civilization. As long as soil erosion on cropland does not exceed new soil formation, all is well. But once it does, it leads to falling soil fertility and eventually to land abandonment. As countries lose their topsoil through
, overplowing, or deforestation, they eventually lose the capacity to feed themselves. Among those facing this problem are Lesotho, Haiti, Mongolia, and North Korea.