| A | B |
|---|
| weathering | occurs when natural forces break down rocks |
| mechanical weathering | breaking up of rocks by physical forces |
| exfoliation | when layers or sheets of rock gradually break off |
| abrasion | wearing something down by friction |
| chemical weathering | breaking up of rocks by chemical reactions |
| humus | decayed organic matter present in soil |
| soil horizon | a layer of soil with different properties than layers above or below |
| soil profile | the soil horizons in one location |
| desertification | the expansion of desert conditions in places where local plants have been destroyed |
