Science: Arizona Arctic

One of the mysteries of geology is why the earth's climate has changed. During some geological ages, the whole earth has been abnormally warm, at other times abnormally cool. This sort of change can be attributed to variations in solar radia tion or some other allover effect. At times, parts of the earth that are now cool had tropical climates, while parts now tropical were covered with ice. The obvious explanation is that the poles and the icecaps associated with them were then in different parts of the earth's-surface, but this theory is hard to prove.

Geophysicist K. M. Creer of Cambridge...

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