Kathy Moriarty, age 11, of Indianapolis, Indiana, for her question:

What do you mean by geological time?

We can clock the passing of time by the sun, the moon or the stars, We also can measure time consuming events right here on the earth. A year, of course, is the time it takes the orbiting earth to pass through its four seasons. The life span of a mountain range is many millions of years. And mountains have a place in the science of geology, the study of the earth's features. Geologists piece together our planet's long history by delving back into the geological events of its past. The time taken by these slow moving events reveals a pattern, a pattern of geological time passing here on earth.

The. pattern of the earth's geological time falls naturally into well defined spans of upheaval followed by spells of rest. These natural divisions are the geological eras. An era may span hundreds of millions of years. Four are finished and the fifth is just begin¬ning. Each immense era is subdivided into several shorter geological periods. The Mesozoic Era of the dinosaurs spans a vast invasion of the sea and the birth of the Rockies and Andes Mountains. The Triassic Period in this era records a geological spell of volcanic uprising in New England.