Eric Fiks, age 13, of Winnipeg, Man., Canada, for his question:

What was the Ordovician period like?

There have been almost a score of geological periods in the age old story of our changeable planet. Each of them lasted through millions of years and Ended in global changes somewhat like the dramatic conclusion of a chapter. And Each was followed by a period of a different character.

The geological eras are named for their types of plants and animals. There are five such eras, and each lasted hundreds of millions of years. Their names suggest the gradual development of life on our Earth. Each Era is subdivided into geological periods, and the periods are named for places. The dinosaurs reached their heyday in the Jurasic Period. Its rock formations and fossils were noticed first in the Jura Mountains of Europe.

The Ordovician period was named for a region in Wales, once inhabited by people ca11ed the ordovices. However, the rocky formations date back millions of years before the arrival of mankind on the earth. This geological period opened some 440 million years ago and closed perhaps 360 million years before the arrival of the human family. It is the second chapter in the immense paleozoic or ancient life Era of the earth's story.

The plants and animals of the remote Ordovician Period were very simple. Our familiar mountains were unborn and even the map of land and sea was different. One phase of geological history is the struggle between the ocean and the continents. Time after time the seas have invaded vast areas of land and finally returned to their basins. The Ordovician Period was a time of triumph for the ocean. More than 60% of the land was under shallow sea water.