Stromatolites are layered structures formed by the activity of microorganisms, primarily cyanobacteria. These ancient formations are among the oldest evidence of life on Earth, dating back over 3.5 billion years. They typically grow in shallow water environments, where the microorganisms trap sediments and minerals, creating distinct layers over time. Today, stromatolites can still be found in certain locations, such as Shark Bay in Australia. They provide valuable insights into early life and the conditions of the Earth's atmosphere and oceans. Studying these formations helps scientists understand the evolution of life and the role of microorganisms in shaping our planet.