Mickey Bennett, age 9, of Dunkirk, Indiana, for his question:

Does wind do more erosion than water?

Running water and weathery winds wear down countless tons of the earth every year. But most of this wearing erosion is done by water. The ground is made of chemical minerals, of soft, silty soils and sturdy rocks. Whenever water touches these minerals, it dissolves away some of their chemicals. Some rocks seem too tough to be dissolved by gentle water. But water, dripping and seeping and running, can wear away the hardest of stones.

Falling rain carries along gritty bits of gravel as it gallops down the mountain slopes. In the valleys, streams wash bits from their banks and when rivers flood, countless tons of precious topsoil are washed away and carried into the sea. All this is water erosion and it goes on everywhere over most of the earth. Winds tend to do their eroding in deserts and gusty canyons, on high slopes and among lofty mountain peaks. Often they wear away boulders in strange shapes and blowing sand may smooth the surface of a high cliff. The most damaging wind erosion occurs on neglected farmland. Roots hold the soil. And a dry, windy drought season can strip away bare, neglected topsoil and turn a whole region into a disastrous dustbowl. This is relatively rare, while water erosion takes its heavy toll of the land every year.