Arthur Young, aged 12, of Toronto, Canada for his question:

What caused such huge glaciers in the Ice Age?

A glacier is made of snowflakes ‑. snowflakes that failed to melt in the summer, A new snowflake is like a tiny lace doily made of ice and air. last year's snowflake is another matter. Its delicate design is crushed and pressed out of shape. Maybe it half melted and froze again into solid ice. Maybe tons of new snow fell and mashed it from above.

This is the kind of old snow that makes a glacier, It’s hard, murky ice, packed solid. Changing seasons crack it and melt its ^­surface. New cold spells freeze the surface still harder. There is never enough warm weather to melt away all this frozen snow. Such glaciers exist on the tops of tall mountains. They also cover the vast continent of Antarctica.

And once upon a time huge glaciers covered all of Canada and the northern part of America. This is the period of time we call the Ice Age. Actually there were several Ice Ages in the dim past. Several times the glaciers crept down from the polar regions and covered the land with glaciers hundreds of feet thick. They last retreated back to the Arctic circle some 25,000 years ago,

Certainly the climate was different in Ice Age days. But it may not have been much cooler in the winters, All a glacier needs to grow is cool summers. Then it can save its supply of snow from one winter to the next. Year by year the sheet of frozen snow grows bigger and bigger.

So, the Ice Age winters need have been no colder than they are now. But the summers must have been cooler. It is estimated that they must have been ten or twelve degrees Fahrenheit cooler than they now are in Canada and the northern part of the United States„ That would be cool enough to save some of last year's snow and build a glacier.

We do not know for sure why the climate changed to make the Ice Ages, Some(say the change was caused by dust and carbon dioxide gas given off by given off by violent volcanoes. This would cloud the air and shut out much of the suns warmth. In any case, summer Finally returned after every lee Age. It must have taken many warm summers to melt the massive glaciers that had collected. For they covered about twelve million square miles with walls of ice.

For a time, the scenery was something like springtime in Canada. Every stream was brimming with crystal ice water. Rivers carried chunks of that melting ice which splits open like bundles of needles. The seas were filled to overflowing and slopped over on the land. Then the new plants sprang up from the rich damp earth. There must have been mosses, hepaticas and trilliums ‑ dust like springtime in Canada.