Going in Reverse (image) The Earth Institute at Columbia University Share Print E-Mail Caption Geomagnetic polarity timescale: Filled and open blocks represent intervals of normal and reverse geomagnetic field polarity over the past 40 million years. Credit Gee and Kent, 2007 Usage Restrictions Credit must be given. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.