Ancient Sediment (image) The Earth Institute at Columbia University Share Print E-Mail Caption Chris Lepre of Columbia University's Lamont-Doherty Earth Observatory (back to camera) precisely dated the artifacts by analyzing layers above, around and below them for reversals in earth's magnetic field. Credit West Turkana Archaeological Project 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.