Flipped Magnetic Poles.

The article discusses a research on frozen magnetism in rocks by Allan Cox, Richard R. Doell and Brent Dalrymple of the U.S. Geological Survey which cites that the direction of the earth's magnetic field was reversed at least twice in the course of geologic time. These conclusions were drawn from a study of old lava flows in many parts of the world, particularly those in Hawaii and those from Mount Enta in Sicily.