Robert Goode, age 11, of Silver Spring, Pennsylvania, for his question:

What really caused the ice age?

This mystery has never been solved. But scientists suggest several possible ex¬planations. Actually, there is evidence that a number. of ice ages have occurred during the long history of the earth. One departed about 700 million years ago„ Another arrived about 100 million years later. Still another came and went about 230 million years ago. Four ice ages have occurred during the past million years or so. So they must be caused by something that has happened more than once.

One theory suggests that the sun's output of energy dwindles from time to time. This could cause cooler climates on earth. Another theory suggests that masses of volcanic dust might screen out the sun's warmth for long periods of time. Either of these changes could reduce the temperature by a few degrees. This would be enough to briny frosty winters with lots of snow. Ice age glaciers could form because the short coolish summers would be unable to melt the accumulation of winter snows.