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This graph shows the strength of Earth's magnetic field over the past 800,000 years.
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Image courtesy of the USGS.

Earth's Magnetic Field Strength - Past 800,000 Years

The strength of Earth's magnetic field changes over the years. Sometimes the magnetic field flips, with the North and South Magnetic Poles trading places. Those "flips" are called magnetic reversals. The last reversal was 780,000 years ago. Is another magnetic reversal going to happen soon?

The graph shows the strength of Earth's magnetic field over the past 800,000 years. The last reversal of Earth's magnetic field was 780,000 year ago. The direction of the magnetic field has been "normal" (meaning "like it is today") since then. This normal period is called the Brunhes normal chron. Before the Brunhes normal chron, the magnetic field was reversed. That time period when the field was reversed is called the Matuyama reversed chron. The graph shows how the strength of Earth's magnetic field has changed during the Brunhes normal. The strength of the magnetic field has gone up and down many times during the Brunhes normal.

In the past there have been many, many reversals of Earth's magnetic field. Sometimes when the field strength fell below 4 there was a reversal... but not all of the time. The field strength has fallen below 4 a few times during the Brunhes normal... but there hasn't been a magnetic reversal.

Some people think we are in the middle of a magnetic reversal right now. The magnetic field has been getting weaker for many years. However, if you look at the graph you can see that the field isn't especially weak. It has been even weaker many times before during the Brunhes normal. Most scientist think it will get stronger in the future, and that this probably isn't a reversal now. Even though we might be in a reversal, we probably are not.

Last modified September 25, 2009 by Randy Russell.

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