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.