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The Spring 2011 issue of The Earth Scientist is focused on modernizing seismology education. Thanks to IRIS, you can download this issue for free as a pdf. Print copies are available in our online store.

Reversals of Earth's Magnetic Field During the Past 160 Million Years

Sometimes Earth's magnetic poles switch places. That is called a magnetic reversal. The graph below shows when magnetic reversals happened in the past. The graph starts (left side) 160 million years ago in the Jurassic Period. There were dinosaurs back then. The right side of the graph shows today.

The black and white stripes along the bottom of the graph show the direction of Earth's magnetic field. Black stripes mean Earth's magnetic field was "normal" (like it is today). White stripes show times when the field was reversed.

Magnetic reversals timeline 160 million years

Did you notice that there isn't much of a pattern? Sometimes the magnetic field goes 40 million years or longer without changing once. Look at the Cretaceous Period around 100 million years ago. Other times the magnetic field changes pretty often. Sometimes it flips back and forth several times within a million years.
Last modified September 21, 2009 by Randy Russell.

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