Reversals of Earth's Magnetic Field During the Past 5 Million Years
Image courtesy USGS. |
This image shows the reversals of Earth's magnetic field over the past 5 million years. The scale along the left is time, going backward from the present as you move down the page, in millions of years before the present day. Chrons are long periods during which the magnetic field remained oriented in one direction for most of the duration of the chron. The current chron, called the "Brunhes normal", began 780,000 years ago. The immediate prior chron was the "Matuyama reverse". Periods during which Earth's magnetic polarity was "normal" (that is, the same as it is now) are shown in black, whereas periods of reversed polarity are shown in white. Most chrons are interrupted by shorter periods, called subchrons, during which the field flips to the opposite of the dominant orientation during the longer parent chron.
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