James Marts, age 12, of Allentown, Pa., for his question:

WHAT EXACTLY IS LAND EROSION?

Our global food supplies depend on surface layers of topsoil, just a few inches thick and limited to certain areas. The planet earth, we are told, already has more people than it can feed. Part of this disastrous situation is land erosion, which steals the topsoil from vast regions of once fertile farm lands.

Erosion means wearing away, and land erosion wears away the surface of the land. It began ages ago as one of nature's projects  and will continue as long as the restless earth has a weathery atmosphere. Nature, however, is a patient and economical housekeeper and her remodeling projects are recycling projects.

The surface of the land changes slowly, as new mountains arise and the oceans and continents shift their positions. Meantime, the restless weather provides winds and water to level the bumps and fill up the hollows. This never ending cycle interlocks with the multitude of life support systems that depend on slim layers of fertile topsoil.

Blustering winds and runny streams help to pulverize rocky minerals. Plants and animals provide organic materials that mix with the minerals to build the fertile soil that supports more plants and animals. In perhaps a century, this patient recycling project adds one inch to a layer of precious topsoil.

Meantime, the restless earth does more remodeling and the blustery weather erodes more topsoil. Bereft of vegetation, winds create dust bowls and the rainy runoff gouges great gullies in the rocky ground. The once fertile land becomes a barren and lifeless region. However, in nature the patient rebuilding and recycling projects continue. New soil is created, old soil is shifted, perhaps dumped into the deltas of flooding rivers.

This planetary project became disastrous when man the¬ farmer needed larger and larger areas of fertile topsoil to feed the expanding human population. But sad to say, he often failed to follow nature's recycling systems for building and rebuilding the soil. To get more farm land, forests were cut down, wild vegetation was stripped away, no natural fertilizers were added to replenish the starving soil. In time the weary land was left to be eroded by the weather.

Now at last, sensible agriculturists have grasped these vital facts of life. Man the farmer is beginning to build and rebuild his soil  and to protect his life giving land from erosion.