Strength of Earth's dipole magnetic field throughout the Brunhes normal chron. Although the field strength has at times fallen below the critical value of 4 which has sometimes triggered magnetic field reversals in the past, no reversal has occurred since the end of the Matuyama reversed chron 780,000 years ago. Numerous named "excursions" (times when the field changed dramatically) are indicated by arrows.
Image courtesy of the USGS.