This graph shows the strength of Earth's magnetic field over the past 800,000 years.
Click on image for full size
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.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

The Magnetic Field

The force of magnetism causes material to point along the direction the magnetic force points. As shown in the diagram to the left, the force of magnetism is illustrated by lines, which represent the force....more

Earth's Magnetic Poles

Earth has a magnetic field. If you imagine a gigantic bar magnet inside of Earth, you'll have a pretty good idea what Earth's magnetic field is shaped like. Of course, Earth DOESN'T have a giant bar magnet...more

The Earth's Magnetic Field

The Earth has a magnetic field with north and south poles. The Earth's magnetic field reaches 36,000 miles into space. The magnetic field of the Earth is surrounded in a region called the magnetosphere....more

The Discovery of the Radiation Belts

The belts of trapped radiation above the Earth's atmosphere, but within the magnetosphere, were first detected by James Van Allen in 1958. Therefore these belts are also known as Van Allen Belts. When...more

Earth's North Magnetic Pole

Earth has a magnetic field with a north pole and a south pole. Earth's magnetic field is pretty much (but not exactly) like the magnetic field around a bar magnet. Earth's North Magnetic Pole (NMP) is...more


Altocumulus clouds are part of the Middle Cloud group (2000-7000m up). They are grayish-white with one part of the cloud darker than the other. Altocumulus clouds usually form in groups and are about...more


Altostratus belong to the Middle Cloud group (2000-7000m up). An altostratus cloud usually covers the whole sky and has a gray or blue-gray appearance. The sun or moon may shine through an altostratus...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA