Reversals of Earth's Magnetic Field During the Past 160 Million Years
|This image shows the reversals of Earth's magnetic field over the past 160 million years. The changing polarity of Earth's magnetic field over time is indicated by the black and white stripes along the bottom of the timeline. Periods of "normal" magnetic polarity (when the field was oriented in the same direction as it is now) are shown as black; times of reversed polarity are shown in white. This timeline runs from 160 million years ago in the Jurassic Period (far left) to the present day (far right).
The "pattern" of reversals is anything but regular. During one span of more than 40 million years in the Cretaceous Period the magnetic field's polarity remained unchanged. At other times, the field has flipped back and forth several times within a million years.
Earth's magnetic field has been in its current alignment, called the Brunhes normal, for the past 780,000 years. Click here for a closer look at magnetic reversals over the most recent 5 million years, or here to see the 5 million year and 160 million year timelines side-by-side.
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