The actions of humans on the soil have had damaging effects beyond current knowledge or ability to repair. Man's destructive relationship with soil can be characterized as parasitic. Classical civilizations collapsed because of destruction of their soil bases. In pursuit of abundant food and fibre, the clearing, tillage, fertilization and pest control methods have depleted soil organic matter, allowed topsoil to erode away, disrupted soil ecosystems, and needlessly poisoned communities of beneficial organisms and groundwater. Each of these factors taken alone reduces the "fertility capital" stored in the soil. Taken together, soil scientists have warned that the synergistic and cumulative effects of the changes unknowingly being in soils may affect life on the planet.