Plate tectonics (IMAGE) University of the Witwatersrand Caption New research indicates that mobile plate tectonics—thought to be necessary for the creation of a habitable planet — was not occurring on Earth 3.9 billion years ago. Credit University of Rochester illustration/Michael Osadciw Usage Restrictions No restrictions. License Public Domain 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.