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 University believes that he has proved it by measuring the magnetism of ancient rocks. Both volcanic and sedimentary rocks, as they are formed, tend to become magnetized by the earth’s magnetic field. Their magnetism, though very feeble, is parallel to the magnetic field that formed it, pointing like a compass needle toward the magnetic pole.

When Dr. Creer measured the magnetism of ancient rocks, he found that it pointed every which way, sometimes toward places that are now near the earth’s equator. Rocks of the same age generally pointed toward the same place, which Dr. Creer believes was the position of the north magnetic pole at the time the rocks were formed. About 700 million years ago, the pole was in Arizona. Then it moved to the Pacific, then to Japan and northward across eastern Siberia to its present position (see map).

Dr. Creer believes that the magnetic and geographical poles always stay close together, so the migrations of the magnetic pole mean that the geographical north pole moved in about the same way, followed faithfully by the earth’s climatic zones. This would explain the ancient icecaps in lands where palms grow now.

None of this means, Dr. Creer points out, that the earth’s axis of revolution has changed its direction in space. More likely, it has stayed put while the thin crust of the earth has slipped around the core, carrying different parts of the surface to the cold polar regions. Dr. Creer is not sure that the crust as a whole has moved. The continents may have drifted independently. By measuring the magnetism of more ancient rocks, he hopes to answer this question too.