Timmy Haley, age 12, of Winston Salem, N.C., for his question:

Why hasn't erosion had time to level the earth?

Suppose you tried to fill a basket of strawberries    while lots of pals kept dipping in their little paws to help themselves. If this sneaky thievery continued to the end of the strawberry season, you could never fill your basket to the brim. On a much grander scale, this is somewhat like global erosion. The winds and rains strive to level the surface bumps, while the earth's crust keeps on creating more ups and downs.

Every season, rains and blustery winds erode rocks from the high peaks and floods wash tons of good topsoil out to sea. The earth's gravity gently pulls most of the loose eroded material down the slopes to the valley floors. This has been going on patiently since the weathery atmosphere came into operation, several billion years ago.

You would think that, in all this time, little by little the yearly forces of erosion would have leveled all the bumps in the dry land and filled all the hollows. After all, we know that during the past 2000 million years, a massive range of mountains in Eastern Canada has been eroded down to gently rolling hills. In the past 300 million years, huge old mountains in Northern Europe have been worn down to their rocky roots.

Certainly the forces of erosion have had time to level the land areas of our planet. Indeed, gravity and the weather have never stopped striv¬ing through billions of years. However, the old earth has other plans. Apparently she prefers wrinkles to a smooth surface. And, you must admit, her mountains,valleys and plains add fabulous sights to the scenery. They also provide a variety of living conditions where multitudes of different plants and animals can enjoy life on the earth.

While erosion toiled at a snail's pace, mighty forces in and below the crust continuously modeled and remodeled the surface. Now and then, there were stupendous mountain building projects around the globe. It take more than 100 million years to complete a massive mountain range.

When a new range jumps up its first little bit, erosion begins at  once. Rains rush down its baby slopes and dump the loose dirt in the hollows. Mountains grow slowly, but thank goodness they rise faster than the forces of erosion can wear them down. At last they reach their full height and stop growing. Then erosion has its way. After a few hundred million years, the proud old mountains are worn down to their roots. But meantime the earth has started a new mountain making project somewhere else.

The forces of erosion strive to bulldoze every hump and fill every hollow. Summer's heat and winter's frost crack the high rocky peaks. Winds hurl gritty sand and erode the faces of tall cliffs. Rains wash all the loosened fragments down the slopes. But the leveling job is never done.  As erosion smooths out one set of wrinkles, the earth creates new ones.