Douglas Anderson, age 10, of Marcel, Minn., for his question:
WHY DO THINGS DECAY?
Thousands of old plants and animals die every day. Suppose they were left on the ground. Soon the world would be knee‑deep in dead bodies and fallen trees. This does not happen because they decay into tiny fragments that provide food for living plants, which provide food for living animals.
When leftover foods go bad, they create a smelly mess. This is one reason why we cover the garbage and send it away to be buried. Actually, this is the first stage of decay. It happens when old food is digested by bacteria, which give off a smelly gas called hydrogen sulphide.
The smelly mess makes us think that decay is something nasty and maybe the world would be better without it. But this is not so. The world is populated by multitudes of plants and animals‑‑from whopping whales to bitsy bacteria. All of them need foods of some sort. But the earth's supplies are limited. There is a limited amount to be shared by all.
This worldwide supply problem is solved by recycling‑by remodeling and reusing old materials again and again. Most of this global recycling is done by the decay process. All plants and animals contribute waste materials to this project which provides their basic supplies.
Maybe the cycle begins with the plants. They use gases plus chemicals from the soil to build complex molecules for building their stems, leaves and such. When leaves fall, they are attacked by bacteria, mites, various insects and armies of other small creatures that live in the soil.
Bit by bit, the old plant cells are used up and broken into small molecules. Some are remodeled to make different molecules. All this is decay, and as the waste material breaks apart it adds new chemicals to the soil. Some of these are the very chemical foods that plants must absorb to build new growth. The decay process also recycles dead and waste animal materials to enrich the soil.
The plant world provides oxygen for all living things. It also provides food for the plant eaters‑‑who provide food for the meat eaters. The dead and waste material from the whole world of plants and animals breaks down and decays. This recycling project provides food chemicals for the next generation of plants‑‑which will provide food and oxygen for the next generation of animals.