Cheryl Parr, age 10, of Cherokee, Oklahoma, for her question:

How old is the world?

Our world is very, very old and nobody knows exactly how many birthdays it has had. It was not easy to trace its age, but scientists now have a rough idea. They say that our world must be almost five billion years old. You can write this down with a figure five and a row of nine zeros. Big figures of this sort are hard to imagine. And nobody alive can possibly imagine all the years that have passed since the earth was created.

However, we do know that the world was very different in past ages. In its early days there were no plants and no animals at all  ¬just bare ground and lots of water. Millions of years later the green plants and a lot of odd looking animals arrived. Later, there were trees and flowering plants. Then the ancestors of our modern animals arrived. And when everything was ready, not so very long ago, the first human family arrived in the world.