Magnetic Poles of Earth

The Earth's magnetic field changes orientation at regular intervals, and although we can't predict when it will happen, we are certain that the poles move. Measurements of the magnetic field over the past 400 years reveal that the North Magnetic Pole has moved around the Arctic north of Canada by as much as six miles per year. In the past 10 years, it picked up speed and began to move north at 25 miles per year.

The historical position of the magnetic poles, going back millions of years, can be read from various magnetic minerals found in lava and other rocks. The minerals show that the magnetic field has reversed direction about every 300,000 years and that more than 780,000 years have passed since the poles last shifted. This makes us long overdue for another magnetic-pole reversal from north to south.

It's not just the magnetic field's orientation that changes over time but also its strength. Analysis of minerals found at the bottom of the ocean shows that the magnetic field has weakened 10 percent since the 19th century.