Bob Hammondi age 11, of Garland, Texas,  or question:

Why doesn’ t the air run out of oxygen?

We breathe oxygen from the air, of course, every minute all our lives. So do all the animals, tame and wild. Trees, plants and even the grass also need oxygen from the air. All the fishes and other creatures in the rivers, lakes and seas need oxygen. They take the oxygen which is mixed with the water just as we take the free oxygen mixed with. the air.

This means that tons of oxygen are being used up every day and if the supply ran out most living things would perish in a few minutes. This tremendous drain on our oxygen supplies is by no mans all. Every fire uses oxygen as a fuel. Even a candle uses a small quota of oxygen from the air. If the worlds oxygen ran out, all burning from furnaces to campfires would also come to an end in a few minutes.

Things have been this way sirce life on earth began, perhaps billions of years ago. During that time, the amount of oxygen used by living things might well equal the weight of the entire earth. Certainly this vast mass of oxygen was not all there at the beginning, either hanging in the air or mixed with the water. Wo know then that we are not gradually using up a fixed supply of oxygen. Actually we do not have to worry about the vital gas running short at all. For Mother Nature provides her creatures with fresh supplies of oxygen every day. We shall not run short of it so long as there are forests of green trees, shrubs, plants and green grass in the world.

The worlds supply of oxygen is supplied by one of Nature's economic cycles and a cycle is something which goes around and around. Our oxygen is used, reprocessed and used again and again. And the reprocessing of oxygen is done by the kingdom of green plants.

We use the oxygen we breathe as a fuel and in the process it is turned into waste carbon dioxide. This waste gas is useless to us and every time we breathe out we pour some of it into the air. However, carbon dioxide is  not a waste gas as far as the green plant world is concerned.  All green plants need carbon dioxide to make their food.

Plants are green because they contain a substance called chlorophyll. This magic fluid uses water from the soil, air and sunlight to manufacture plant sugar, the basic foodstuff from which all plant parts are made. In the process of making sugar, the carbon and some of the oxygen is used from the carbon dioxide gas. Some oxygen is left over from the recipe as a waste product.

The oxygen is poured out from every green leaf during daylight hours. Some, but far from all of it, is used by the plants themselves. The rest is waste as far as the plants are concerned. Tons of this reprocessed oxygen are added to the air every day and wafted by the breezes around the world. We breathe it, the animals breathe it, and in the process return carbon dioxide to the air. The cycle goes on and on. So long as there are plants, green forests and meadows; the air will got fresh supplies of oxygen every day.