Shirlene Adams, age 11, of Phoenix, Arizona, for her question:

 How old is the earth?

Some experts think that our beautiful earth is about 3,000 million years old, some believe the grand old lady may be nearer 4,000 million years old. From these figures we now estimate that the world has had between three billion and four billion birthdays. But only the earth knows the exact number. And, like most lovely ladies, she leaves us guessing. However, our scientists have clues to help them make a reasonable guess at the age of the earth.

For one thing, the geologist can read the earths diary. Yes, the proud old lady has kept a diary which dates back millions and millions of years. It was written as she formed the rocky layers of her crust. The whole history of mankind is but a moment in the history of the world. In a lifetime, we have no time to notice many changes on the face of the earth. But actually the surface of the earth is restless and very changeable.

Suppose we could telescope the 3,000 or 4,000 million years into a single day. The earth would seem to be a boiling pot of soup. Mountains would rise and fall in hours, seas would slop over the lands and retreat in moments. Volcanoes would spit like bubbles, lakes would fill and dry up in seconds. The Ice Ages would come and go in minutes.

All these dramatic events left their scars on the face of the earth. The experts can tell which rocks were made by seawater and which were made by volcanoes. They can date these events and tell when the rocks were clawed by Ice Age glaciers. For these are the rocky pages of the old earth's diary.

The earth seems proud of the creatures that lived and died on her surface. For she keeps specimens pressed between the rocky pages of her diary. The experts can date these fossils and chart the story of life on earth.

Lately, radioactive materials have boon used to date the earth. An isotope of carbon can give the exact age of a fossil up to 35,000 years. The rocks can be dates by a uranium mineral called, uranite. So far, the oldest rock dated by this method revealed its age to be 2,200 million years. Allowing for older rocks still undiscovered, we may be sure the earth has had a solid crust for some 3 billion years. Some experts believe the earth was in a molten state perhaps a billion years before it became solid.

In her babyhood, the earth's face seems to have been covered with a rash of lively volcanoes. Then came rains which deluged onto the seething rocks and filled the air with steam. Things became calmer and the teeming rains flowed down to fill the seas. In these ancient seas, the miracle of life began.

The first small creatures left evidence of their existence in rocks formed 2,000 million years ago. Life developed slowly, adjusting to the changing earth. Some 300 million years ago, plants and animals invaded the bare rocks of the land. Slowly, through countless changes, the earth clothed herself in a green mantle and populated her surface with countless creatures. For a planet, she may be still in her youth, with many billions of years of changes still ahead.