North American Craton (IMAGE) University of California - Berkeley Caption This graphic shows the thickness (in kilometers) of the North American lithosphere. The blue area is about 250 km thick and, based on new findings reported in <i>Nature</i>, is composed of a 3-billion-year old craton underlain by younger lithosphere deposited as ocean floor subducted under the continent within the past billion years. The green, yellow and red areas are younger and thinner continental lithosphere added around the margins of the original craton, also by subducting sea floor. The thick broken line indicates the borders of the stable part of the continent. Credit Barbara Romanowicz and Huaiyu Yuan, UC Berkeley Usage Restrictions None License Licensed content 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.