Earth is a giant magnet. It has a north and south magnetic pole. It also has a magnetic field called the magnetosphere.   Magnetic Field Reversals:  Earth's magnetic poles have switched places repeatedly over the past hundreds of millions of years, each time reversing Earth's magnetic field. Scientists don't know for certain why magnetic reversals occur, but there is hard evidence showing that they have occurred. The evidence comes from rocks on the ocean floor. At the center of ridges on the ocean floor, hot magma pushes up through the crust and hardens into rock. Once the magma hardens,... Show more

Earth is a giant magnet. It has a north and south magnetic pole. It also has a magnetic field called the magnetosphere.
 

Magnetic Field Reversals:  Earth's magnetic poles have switched places repeatedly over the past hundreds of millions of years, each time reversing Earth's magnetic field. Scientists don't know for certain why magnetic reversals occur, but there is hard evidence showing that they have occurred. The evidence comes from rocks on the ocean floor. At the center of ridges on the ocean floor, hot magma pushes up through the crust and hardens into rock. Once the magma hardens, the alignment of magnetic domains in the rock is frozen in place forever. The newly hardened rock is then gradually pushed away from the ridge in both directions as more magma erupts and newer rock forms. Rock samples from many places on the ocean floor reveal that magnetic domains of rocks from different time periods are aligned in opposite directions. The evidence shows that Earth's magnetic field reversed hundreds of times over the past 330 million years. The last reversal was less than a million years ago.

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