Reversals of Earth's Magnetic Field During the Past 160 Million Years
Sometimes Earth's magnetic poles switch places. That is called a magnetic reversal. The graph below shows when magnetic reversals happened in the past. The graph starts (left side) 160 million years ago in the Jurassic Period. There were dinosaurs back then. The right side of the graph shows today.
The black and white stripes along the bottom of the graph show the direction of Earth's magnetic field. Black stripes mean Earth's magnetic field was "normal" (like it is today). White stripes show times when the field was reversed.
Did you notice that there isn't much of a pattern? Sometimes the magnetic field goes 40 million years or longer without changing once. Look at the Cretaceous Period around 100 million years ago. Other times the magnetic field changes pretty often. Sometimes it flips back and forth several times within a million years.
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