Geophysics: What Caused the Cold?

Scientists have learned much about the great glaciers of the Pleistocene epoch—the slow ice masses that spread several times across much of the globe, killing off thousands of animal species and stimulating the evolution of man.

But what caused the periodic cold? There is no evidence that the sun has any cyclic activity that might have brought it on, nor can it be blamed on any other astronomical effect.

Explanatory theories have never been wholly convincing, but scientists keep trying. Now, in the magazine Na ture, Dr. Alexander T. Wilson of New Zealand's Victoria University of Wellington offers an intriguing solution....