Bret Miller, age 10, of Tacoma, Wash., for his question:

HOW DO ROCKS TURN INTO SOIL?

This is a long story of the earth's sensible ecology systems. It is especially interesting at this time because it is directly related to the food problems of our hungry world. In fact, it is the basic key to our frantic famine situation. For our food depends on plants that feed us and the animals that provide our meat and dairy products. And the plants depend on healthy soil.

Powdered rock is a basic ingredient in the soil, but it is not the whole recipe. Soil is a balanced mixture of crumbled rocky minerals blended with the decaying wastes and remains of both plants and animals  living and dead. Finally this miraculous mixture of healthy soil is populated with bugs and grubs and wormy animals, plus a vast assortment of creatures too small to mention.

However, though all these other ingredients are necessary, the basic soil making recipe does indeed begin those powdery nonliving minerals. And these are taken from the sturdy nonliving rocks of the earth's crust. It is possible, as you probably know, to smash up some of the softer rocks with a hammer. But our patient planet uses other methods  on a global scale.

The sun, which causes the changing weather, also helps. So does the moon, which causes the tossing tides. So does the earth's mighty gravity, which drags great boulders down the mountains and makes the streams run down the slopes. So do the changing seasons, when summer heat and icy frost cause great rocky slabs to stretch and shrink and crack apart.

All these forces work together to weaken the rocky crust. Ice and heat create cracks; running water dissolves and washes away the rocky minerals. Step by step great slabs are broken into big boulders, and big boulders are smashed into pebbles and crumbly debris. Meantime, the rains and running rivers erode the fragments into powdery dust.

Here and there birds and other animals leave organic wastes which get mixed with the inorganic minerals. Finally the mixture is invaded by the mini dirt dwellers that turn the whole thing into living, healthy soil.

No wonder it takes the patient earth 100 years to build a one inch layer of healthy soil. However, man can do the job much faster  if he copies earth's own basic recipe. This is why the care and rebuilding of soil is the sane solution to our food supplies.