Fossil plankton 1 (IMAGE) University of Leicester Caption Fossil plankton from half a billion years ago. These tiny algae measure much less than a millimetre in size. They evolved their colonial structure to avoid being eaten by early animals. Credit: THP Harvey Credit THP Harvey Usage Restrictions Use only with credit. License Original 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.