Carolyn Yip  age 9  of Victoria, B.C., or her question:

What caused the Ice Age?

Canada was buried under glaciers two miles thick. Sheets of more ice covered New England, all the Great Lakes region and much of Europe. Glaciers amassed In valleys and on high mountains still further south. They gouged lakes and valleys, rounded hilltops, skuffed furrows in hard rocks and toted boulders and debris for hundreds of miles,

The tracks tell us where the glaciers went. We also know when they came. Ice Ages gripped the world four times in the past million years. Still others came and went in the dim past.  We do not know for certain what caused them, experts have theories, good ideas with reasonable evidence. So fare no theory explains all the facts,

Glaciers grow where summers are too cool to melt the winter snowfall. The climate may not have been very cold, But summers must have been cool enough to leave some of winter's snow. Year by year, the snow piled and packed into hard, icy glaciers, Only a 10 to 12 degree drop in temperature could have caused the Ice Ages.

Dust and carbondioxide in the air steals the sun's heat„ One theory suggests violent volcanoes threw up enough dust to cool the climate, Another suggests that the continents rose up high into cooler air, These are early theories and few experts accept them.

A very complex theory takes three different facts into account. It is called the astronomical theory because it is based on how the earth moves. The earth spins on its axis and moves around the sun. Over long cycles, there are slight changes in these earth movements.

The earth's axis is not at right angles to its orbit around the sun. This makes the north pole tip towards the sun in summer and away in winter. The slant of the sun's rays alter, giving us the seasons. The angle of earth's axis changes in cycles of 40,000 years. The slanting winter rays could be even longer during part of that long cycle.The earth's orbit varies in cycles of 91 800 years. At certain times in that long cycle the earth is further from the warm sun. The orbit is slightly oval; This varies in cycles of 21,000 years,

All these changes are very slight, one alone could not cause an lee Age. But at times they work together. Experts have plotted curves of the cycles. The worst has happened four times in the past 60,000 years. This fine complex theory falls down when the rocks prove the Ice Ages came and went during the past million years!

Another theory blames the Ice Ages on the sun. More sunspots and solar cyclones could cool the earth by cooling the sun. But there are no facts to show the sun ever had such a cool spell.

There were long warm spells between the past four Ice Ages, The last began to retreat only 401000 years ago. We may be living in one of those warm between stages. Our ancestors met and coped with those glaciers and should they come again, we can do as well, or even better, than they did.