Sometimes Earth's magnetic poles switch places. That is called a magnetic reversal. These graphs show how often magnetic reversals happen. Black stripes show times when Earth's magnetic field was "normal" (like it is today). White stripes show times when the field was reversed. The graph on the left shows the past 160 million years. The graph on the right shows a close-up of the past 5 million years.
Images courtesy of the USGS.