Strength of Earth's dipole magnetic field throughout the Brunhes normal chron. Click on image for full size (64 Kb) Image courtesy of the USGS.

The strength of Earth's magnetic field fluctuates over time. Occasionally 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. Are we due for another reversal soon?

The graph shows the strength of the dipole portion of Earth's magnetic field over time. The strength of the dipole moment is given in units of 10²² Amperes-meters². The last reversal of Earth's magnetic field was 780,000 year ago. The period of "normal" (meaning "like it is today") polarity of Earth's field since that reversal is known as the Brunhes normal chron. The Brunhes normal was proceeded by the Matuyama reversed chron, during which time Earth's magnetic poles were opposite their current orientation. The graph shows how the strength of Earth's dipole field has risen and fallen numerous times throughout the Brunhes normal chron.

The dashed line at a dipole strength of 4 x 10²² A m² is a threshold for magnetic reversals noted by some scientists. In the past, magnetic reversals have sometimes occured when the dipole field strength dropped below this critical value. Note, however, that the field strength has fallen below 4 several times during the Brunhes normal without ushering in a reversal.

Some people have speculated that we are currently on the verge of another reversal. Although it is true that the strength of the dipole field has been declining for many years, one can see on the graph that the field has been considerably weaker than its current value (around 6) numerous times during the Brunhes normal... without triggering a reversal. Even though it is indeed possible that we are in the midst of a reversal, it seems more likely that this is just another temporary reduction in dipole field strength like so many that preceded it.

This graph shows the strength of Earth's magnetic field over the past 800,000 years. Click on image for full size (64 Kb) Image courtesy of the USGS.

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.

This graph shows the strength of Earth's magnetic field over the past 800,000 years. Click on image for full size (64 Kb) Image courtesy of the USGS.

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. 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.

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.