Steve Miller, age 9, of San Francisco, California, for his question:

What is the smallest form of life on earth ?

Three hundred years ago, most people thought that the smallest living thing was fly, a flea or maybe a tiny mite. They were sure that the smallest living things were not too small to be seen. Then, in 1675, Anton van Leeuwenhoek spotted some minute wigglers under his microscope. He named them animalcules thinking they were minute living things which they were.

We cell them microbes and our more powerful microscopes have added 100,000 different kinds to the 27 animalcules described by Leeuwenhoek. We think of living things as being able to feed: grow and multiply themselves   which makes the microbes very much alive indeed.

The amount of food. a microbe can eat is enormous, The items on its menu may be amazing and, to us, often repulsive. A microbe can eat twice his own weight in food every two hours. And he will eat day and night without stopping so long as his favorite food holds out,

Nor would he be joking if he said he could eat a horse. For the job of breaking up the bodies of decaying animals and rotting leaves is done by billions of hungry little microbes. They have special digestions which turn these waste materials into simple chemicals which can be used again by plants. Other microbes break up the food we eat into substances which we can digest. Yes, colonies of these little helpers live right in our insides., They love their work and we couldn’t manage without them.

Compared with microbes, rabbits are slow multipliers. Among members of the microbe family are the yeasts and we know exactly how fast they can multiply when food is plentiful. In ten hours, if the temperature is right and the food plentiful,. five pounds of yeast will multiply into 25 pounds of yeast. This bulky weight is made up of billions of individual yeast cells   smallest relatives of the mushroom. It takes a rabbit several weeks to produce each batch of bunnies.

And microbes do not grow old and die. Their life span lasts until some poison or enemy destroys them, If food runs outs they simply put themselves into storage till a new supply arrives They multiply by simply dividing in two  each small half grows till it is full sized. That way there are no parents and no children no family life,

Microbes come in a huge variety of shapes and sizes. Compared with the visible creatures, some are as big as whales and others as small. as mice. Side by side, about 25,000 of them would measure an inch, find they populate the whole world. They crowd on every leaf and patch of skin. They ride the air on every speck of dust. They inhabit our food and our insides.

No screen could possibly keep out the microbes   and this is a good thing. Only a few of them are harmful to us. Life for us without the help of earth's smallest living things would be down right impossible,