Cuatro Ciénegas Stromatolite (IMAGE) Rice University Caption Bacteria in the pozas form coral-like "stromatolites" that are geologically identical to 3.5 billion-year-old fossils that are believed to be the oldest evidence of life on Earth. Credit Tommy LaVergne/Rice University Usage Restrictions must credit: 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.